GIFT  OF 


...  v.' 


WJBI'IZWIH 
*  -NT 


6  1888 


CONCLUSIONS 


ADOPTED  BY  THE 


FEENCH    COMMISSION 


IN  REFERENCE  TO 


TESTS  OF  CEMENTS. 


THE 


INFLUENCE  OF  SEA  WATER 


HYDRAULIC  MORTARS. 


TRANSLATIONS  FROM 
THE  FRENCH  AND  FROM  THE  GERMAN  BY 


O.  M.  CARTER, 

CAPT.,  CORPS  OF  ENGINEERS,  T 


E.  A.  GIESELER, 

I  A  N  T     E  N  li  I  N  E  E  II. 


WASHINGTON: 

GOVERNMENT   PRINTING   OFFICE. 

1897. 


CONCLUSIONS 


ADOPTED  BY  THE 


FKENCH    COMMISSION 


IN  REFERENCE  TO 


TESTS  OF  CEMENTS. 


THE 

INFLUENCE  OF  SEA  WATER 


ON 


HYDKAULIC  MORTARS. 


TRANSLATIONS  FROM 
THE  FRENCH  AND  FROM  THE  GERMAN  BY 

O.  M.  (CARTER,  ^  E.  A.  GIESELER, 

CAPT.,  CORPS  OF  ENGINEERS,  U.  S.  A.,  TJ.  S.  ASSISTANT  ENGINEER. 


WASHINGTON: 
GOVERNMENT  PRINTING   OFFICE. 

1897. 


WAR  DEPARTMENT. 

DOCVMEXT  No.  36. 
OFFICE  OF  THE  CHIEF  OF  ENGINEERS. 


OFFICE  OF  THE  CHIEF  OF  ENGINEERS, 

UNITED  STATES  ARMY, 
Washington,  D.  C.,  Aprils,  1897. 

SIR  :  I  have  the  honor  to  submit,  herewith,  translations  by  Capt. 
O.  M.  Carter,  Corps  of  Engineers,  United  States  Army,  and  Mr. 
E.  A.  Gieseler,  United  States  Assistant  Engineer,  of  the  following- 
named  papers : 

1.  Conclusions  adopted  by  the  French  Commission  in  reference 
to  Tests  of  Cements. 

2.  The  Influence  of  Sea  Water  on  Hydraulic  Mortars.     By  Dr. 
William  Michaelis. 

3.  The  Influence  of  Sea  Water  on   Hydraulic   Mortars.     By 
Union  of  German  Portland  Cement  Manufacturers. 

4.  The  Influence  of  Sea  Water  on  Hydraulic  Mortars.     By  E. 
Candlot. 

These  papers  contain  information  of  great  value  to  officers  of 
the  Corps  of  Engineers,  and  I  recommend  that  authority  be  granted 
to  have  them  printed  at  the  Government  Printing  Office  (in  one 
volume),  and  that  five  hundred  copies  be  obtained  for  the  use  of 
the  Engineer  Department,  upon  the  usual  requisition. 
Very  respectfully,  your  obedient  servant, 

JOHN  M.  WILSON, 
Brig.  Gen.,  Chief  of  Engineers, 

United  States  Army. 
Hon.  R.  A.  ALGER, 

Secretary  of  War. 


[First  indorsement.] 

WAR  DEPARTMENT,  April  9,  1897. 
Approved. 

By  order  of  the  Secretary  of  War : 

JOHN  TWEEDALE, 

Chief  Clerk. 

(3) 


371950 


CONTENTS. 


Page. 

1.  Conclusions  adopted  by  the  French  Commission  in  reference  to  Tests 

of  Cements 7 

2.  The  Influence  of  Sea  Water  on  Hydraulic  Mortars.     By  Dr.  William 

Michaelis 37 

3.  The  Influence  of  Sea  Water  on  Hydraulic  Mortars.     By  Union  of  German. 

Portland  Cement  Manufacturers 63 

4.  The  Influence  of  Sea  Water  on  Hydraulic  Mortars.     By  E.  Candlot 69 

(5) 


CONCLUSIONS  ADOPTED  BY  THE  FRENCH  COMMISSION  IN 
REFERENCE  TO  TESTS  OF  CEMENTS. 


INTRODUCTION. 

A  technical  commission  having  for  its  object  "to  formulate  uni- 
form rules  to  be  followed  in  testing  construction  materials  and  to 
determine  the  units  which  should  be  assumed  for  a  basis  of  com- 
parison "  was  constituted  under  the  direction  of  the  ministry  of 
public  works  of  France  by  a  decree  of  November  9,  1891.  That 
decree  specifically  instructed  one  of  the  two  sections  of  the  com- 
mission, Section  B,  to  make  a  study  of  the  questions  relating  to 
materials  of  construction  other  than  metals.  At  the  first  meeting, 
presided  over  by  Inspector  General  Guillemain  (December  28, 1891), 
a  certain  number  of  members  were  formed  into  a  committee  which 
proceeded  to  make  investigations  and  experiments  and  to  formulate 
conclusions.  That  committee  confined  itself  to  a  study  of  the 
methods  of  testing  masonry  materials,  namely,  cements,  limes,  poz- 
zuolanas,  sands,  and  plasters.  Those  studies  were  the  object  of  its 
deliberations  during  twenty-nine  meetings  held  between  the  28th 
of  December,  1891,  and  the  5th  of  May,  1893,  at  the  ministry  of 
public  works,  and  most  of  the  questions  arising  in  the  course  of  the 
discussion  were  submitted  to  the  study  of  a  subcommittee,  then 
treated  in  special  reports. 

The  labors  of-  the  committee  were  finally  communicated  to  the 
members  of  the  section,  which,  at  its  meeting  on  May  8,  1893,  defi- 
nitely adopted  the  conclusions  to  be  submitted  to  the  full  com- 
mission. The  present  report  has  for  its  object  to  sum  up  those 
conclusions  in  a  methodical  order  and  to  give  as  succinctly  as 
possible  the  considerations  which  led  to  their  adoption. 

GENERAL  CONSIDERATIONS. 

§  1.  CHOICE  OF  TESTS. 

Several  members  of  the  section  were  of  opinion  that  the  end  to 
be  obtained  was  to  seek  among  all  of  the  tests  now  in  use  a  small 
number  which  could  be  recommended  for  determining  the  quality 
of  materials.  The  section  would  then  be  able  to  formulate  some 
clear,  precise  rules  which  could  be  followed  for  receiving  materials. 
There  would  be  avoided  the  definition  of  a  considerable  number  of 
tests  from  which  only  doubtful  information  concerning  the  value 
of  the  products  could  be  obtained,  and  whose  very  diversity  would 
be  opposed  to  the  "  unification"  which  was  the  object  of  the  labors 
of  the  commission. 


10  TESTS   OF   CEMENTS. 

The  majority,  however,  diet 'not  think  it  proper  to  adopt  that 
view. 

On  the  one  hand  it  would  not  be  possible  in  the  present  state  of 
our  knowledge  of  masonry  materials  to  affirm  that  such  and  such 
tests  are  necessary  and  sufficient  to  characterize  in  a  general  man- 
ner good  products,  and  it  should  be  observed  on  the  other  hand 
that  the  different  tests  to  which  a  product  is  submitted  are  intended 
to  show  whether  it  possesses  properties  suitable  for  the  special  use 
to  which  it  is  to  be  put.  For  certain  constructors  who  wish  to 
make  use  of  a  cement  for  temporary  sea  works  rapidity  of  set  will 
be  of  prime  importance,  and  strength  at  the  end  of  some  months 
comparatively  unimportant.  For  others,  on  the  contrary,  who  are 
making  conduit  pipes,  rapidity  of  set  is  of  no  special  interest, 
while  ultimate  strength  is  a  matter  of  the  utmost  importance. 

Those  two  examples,  which  can  be  readily  multipled,  suffice  to 
show  that  a  certain  test,  indispensable  in  one  case,  becomes  useless 
in  another,  and  that  consequently  the  task  of  the  commission  would 
not  be  completely  fulfilled  if  it  left  out  any  one  of  the  tests  now 
used  unless  that  test  fails  to  furnish  any  information  whatever  con- 
cerning the  properties  sought.  Hence,  each  observer,  according 
to  the  conditions  which  the  materials  must  fulfill,  is  permitted  to 
make  a  choice  among  the  tests  which  he  believes  it  useful  to  make. 
Some  members  have  expressed  an  opinion  that  a  distinction  should 
be  made  between  working  tests  and  laboratory  tests,  the  first  being 
simple,  practical,  rapid,  and  sufficient  for  the  ordinary  conduct  of 
works ;  the  others  of  a  more  scientific  character,  requiring  more 
complicated  apparatus,  more  experienced  operators,  and  experiments 
lasting  over  a  greater  length  of  time.  That  view,  however,  was 
not  adopted  by  the  section.  To  the  reasons  which  led  to  abstain- 
ing from  expressing  a  preference  for  any  particular  test  it  should 
be  added  that,  generally,  the  methods  to  be  employed  can  not  be 
simplified  except  to  the  detriment  of  exactitude;  that  it  would  be 
difficult  to  make  one  classification  of  working  tests  and  another  of 
laboratory  tests,  the  personnel  and  the  apparatus  varying  consid- 
erably according  to  locations ;  and  finally,  once  a  method  of  test 
is  decided  upon  there  is  no  reason  why  it  should  not  be  conducted 
with  all  of  the  resources  which  are  at  the  disposal  of  the  operator 
in  the  particular  case. 

§2.  STANDARD  TESTS. 

The  tests  now  used  relate,  some  to  binding  media  in  a  pulverized 
condition,  others  to  the  same  materials  gauged  with  water  or  with 
water  and  sand  to  form  pastes  or  mortars.  * 


*  The  name  paste  is  given  generally  to  products  resulting  from  gauging  bind- 
ing media  with  water,  and  the  name  mortar  to  products  resulting  from  gauging 
them  with  water  and  sand. 


TESTS   OF   CEMEXTS.  11 

Such  tests  can  have  for  their  aim  to  seek  either,  given  a  certain 
binding  medium,  what  results  can  be  realized  by  employing  it  in 
such  or  such  conditions,  or,  given  several  binding  media,  which 
among  them  will  best  satisfy  the  special  objects  in  view. 

Thus,  a  constructor  having  at  his  disposal  a  cement  of  a  cer- 
tain quality  for  the  manufacture  of  the  masonry  of  a  work,  can 
make  tests  for  the  purpose  of  determining  what  mixtures  will  be 
the  most  advantageous,  having  regard  to  the  conditions  under 
which  the  mortar  will  be  placed ;  or,  having  at  the  time  of  formu- 
lating specifications  a  choice  between  such  or  such  limes  or  cements, 
he  will  require  of  the  manufacturers  or  he  will  have  made  tests 
capable  of  showing  such  qualities  of  the  competitive  products  as 
will  enable  him  to  select  one  of  them  with  a  perfect  knowledge  of 
the  reasons  for  such  selection.  To  satisfy  such  double  object  the 
methods  adopted  in  the  different  tests  should  apply  to  the  most 
general  case,  that  in  which  any  mortar  whatever  is  submitted  to 
test ;  but  for  each  test  it  will  be  necessary  to  specify  definitely  the 
mixture,  the  conditions  of  manufacture,  of  preservation,  and  the 
age  of  any  special  mortar  tested,  in  order  to  obtain  comparable  re- 
sults which  may  serve  to  characterize  the  products  tested.  When 
operations  are  conducted  on  a  special  mortar  the  test  is  called  a 
standard  test. 

Suppose,  for  example,  it  is  desired  to  indicate  the  method  to  be 
followed  in  tests  of  rupture  by  tension :  There  will  be  specified  the 
form  of  the  briquette  as  well  as  the  arrangement  of  the  apparatus 
to  be  employed  for  determining  the  resistance  of  any  mortar  what- 
ever, and  there  will  be.  added  that  the  standard  test  will  be  con- 
ducted on  a  mortar  having  been  manufactured  and  preserved  under 
such  or  such  conditions.  It  is  the  results  of  standard  tests  that 
manufacturers  will  probably  be  required  to  publish,  when  they 
wish  to  make  known  the  quality  of  their  products.  It  is  also  to 
the  standard  test  that  reference  is  generally  made  in  specifications 
for  furnishing  binding  media,  because  once  the  rules  relative  to 
those  tests  are  adopted  in  the  laboratories,  the  competitors  will  be 
able  to  determine  what  conditions  must  be  satisfied  in  each  case  as 
easily  as  the  consumers  can  verify  whether  the  conditions  exacted 
are  fulfilled.  For  each  one  of  the  tests  relating  to  hydraulic  mor- 
tars the  special  rules  governing  the  standard  test  will  be  indicated 
immediately  following  the  general  rules  defining  the  methods 
recommended  by  the  section. 

§  3.  CLASSIFICATION  OF  PRODUCTS  FROM  RESULTS  OF  TESTS. 

The  object  of  the  labors  of  the  commission  is  clearly  defined,  as 
well  as  by  the  decree  which  constituted  it  as  by  the  discourse  de- 
livered by  President  Picard  on  assuming  office,  and  it  would  be 


12  TESTS    OF    CEMENTS. 

useless  to  revert  to  it  had  not  various  members  of  the  section,  on 
different  occasions,  expressed  doubts  on  the  subject.  In  their 
opinion  the  labors  of  the  commission  would  not  fulfill  completely 
the  expectations  of  those  interested  in  the  manufacture  and  use  of 
masonry  materials  if,  in  connection  with  the  best  methods  of 
testing,  there  were  not  given  results  or  figures  characterizing 
various  products  of  good  quality.  The  section  considers  that  the 
commission  would  exceed  its  powers  if  it  specified  the  conditions 
which  should  be  fulfilled  by  materials  in  order  to  be  classed,  with 
respect  to  their  commercial  value,  as  belonging  in  such  or  such  a 
category.  Although  the  commission  would  be  in  a  position  to 
determine  those  conditions  perfectly,  that  is  to  say,  to  draft  speci- 
fications for  the  acceptance  of  binding  media  of  various  kinds,  it 
is  certain  that  a  number  of  clauses  would  have  to  be  varied  accord- 
ing to  the  nature  of  the  works  to  be  executed.  For  a  slow-setting 
cement,  for  example,  it  should  be  stipulated  in  certain  cases  that  it 
should  set  in  less  than  six  hours,  although  in  other  cases  there 
would  be  no  reason  for  the  same  delay ;  a  resistance  of  20  kilograms 
per  square  centimeter  at  the  end  of  seven  days  would  be  necessary 
for  certain  work,  while  for  others  the  same  resistance  at  the  end 
of  a  month  would  suffice.  Thus,  for  any  well-defined  class  of 
products  the  conditions  to  be  inserted  in  type  specifications  could 
not  be  given,  and  it  is  always  to  the  consumer  that  finally  will  fall 
the  task  of  specifying  those  conditions,  reference  being  had  to  the 
conditions  which  a  product  must  fulfill  and  the  results  which  the 
progress  of  manufacture  permit  to  be  realized.  As  to  the  com- 
mercial value  of  products,  it  should  be  based  on  numerous  elements 
of  quality.  If  we  take  the  example  which  has  just  been  cited  there  is 
no  reason  for  assuming  that  a  cement  which  after  having  hardened 
slowly  has  acquired  at  the  end  of  a  relatively  long  time  a  great 
resistance,  is  of  a  quality,  and  consequently  of  a  value,  superior  or 
inferior  to  that  of  a  cement  of  the  same  nature  which  after  having 
hardened  more  quickly  has  acquired  at  the  end  of  an  equal  lapse 
of  time  a  less  resistance. 

The  labors  of  the  commission  have  therefore  been  limited  for 
good  reasons  to  a  choice  of  methods  of  test,  without  specifying  a 
classification  of  products  from  results  furnished  by  a  series  of  tests. 

§4.  CLASSIFICATION  OF  HYDRAULIC  BINDING  MEDIA. 

If  the  plan  of  assuming  as  a  basis  of  classification  the  quality  of 
hydraulic  binding  media  of  the  same  nature  was  rejected  unhesita- 
tingly, the  question  as  to  whether  it  was  possible  to  proceed  to  a 
classification  of  those  materials  was  discussed  at  length. 

Several  members  of  the  section  maintained  that  such  classifica- 
tion had  been  adopted  by  the  conventions  of  Munich  in  1884,  and 


TESTS    OF    CEMENTS.  13 

of  Dresden  in'  1886,*  and  had  been  brought  to  the  attention  of  the 
International  Congress  held  in  Paris  in  1889 ;  that  such  a  classifica- 
tion would  have  the  advantage  of  preventing  the  sale  of  the  most 
diverse  products  under  identical  names,  which  would  favor  con- 
sumers ;  and,  moreover,  that  it  is  necessary,  in  order  to  employ 
the  methods  of  test  recommended  by  the  commission,  that  it  should 
be  known  at  least  on  what  substances  the  test  should  be  made. 

The  majority  of  the  section  has  noted  the  difficulties  that  would 
be  met  immediately,  as  well  from  the  technical  as  from  the  com- 
mercial point  of  view,  if  that  attempt  were  made.  From  the  techni- 
cal point  of  view  the  choice  of  a  satisfactory  basis  of  classification 
would  be  a  very  delicate  one.  Reliance  could  not  be  placed  upon 
the  essential  properties  of  the  products,  since  those  properties, 
often  common  to  products  of  very  different  natures,  have  no  rela- 
tion to  each  other,  and  none  of  them  can  be  considered  as  character- 
istic. Neither  would  chemical  composition  be  a  certain  criterion. 
There  is  not  yet  sufficient  information  as  to  the  grouping  of  the 
elements  which  constitute  hydraulic  binding  media ;  even  for  those 
media  which  present  qualities  most  nearly  alike  the  proportion  in 

*(1)  Hydraulic  limes  are  products  obtained  by  the  calcination  of  limestones 
containing  more  or  less  clay  or  silicic  acid,  and  which,  sprinkled  with  water,  are 
slaked  entirely  or  partially  into  powder.  According  to  local  circumstances,  the 
lime  is  delivered  in  commerce  in  the  form  of  lumps,  or,  hydrated,  in  the  form  of 
powder. 

(2)  Roman  cements  are  products  obtained  by  the  calcination,  below  the  verge 
of  vitrification,  of  marl  containing  much  clay.    They  do  not  slake  when  sprinkled 
with  water,  and  it  is  necessary  to  employ  mechanical  means  to  reduce  them  to 
powder. 

(3)  Portland  cements  are  products  obtained  from  the  calcination,  up  to  the 
verge  of  vitrification,  of  natural  marl,  or  of  artificial  mixtures  of  substances  con- 
taining clay  and  lime.     They  are  reduced  to  powder  by  grinding,  and  contain  at 
least  1. 7  parts,  by  weight,  of  lime  for  1  part  of  material  which  gives  to  the  lime  its 
hydraulic  property.     To  regulate  certain  properties  of  technical  importance, 
there  may  be  added  foreign  material  up  to  2  per  cent  of  the  weight  without  this 
addition  necessitating  any  change  of  name. 

(4)  Hydraulic  gangues  are  natural  or  artificial  materials  which  generally  do 
not  harden  under  water  when  alone,  but  only  when  mixed  with  caustic  limes. 
Such  are  pozzuolana,  santorin  earth,  trass  obtained  from  certain  volcanic  tufa, 
furnace  slag,  burnt  clay,  etc. 

(5)  Pozzuolana  cements  are  products  obtained  by  intimately  mixing  powdered 
hydrates  of  lime  with  hydraulic  gangues,  ground  to  the  fineness  of  dust. 

(6)  Mixed  cements  are  products  obtained  by  intimately  mixing  manufactured 
cements  with  suitable  extraneous  material.     Such  binding  media  should  be 
formally  designated  as  mixed  cements,  with  an  indication  of  the  materials 
entering  into  their  composition. 

It  was  remarked  at  the  congress  of  1889  that  the  preceding  nomenclature  does 
not  comprise  fat  or  thin  limes,  makes  no  distinction  between  more  or  less 
hydraulic  limes,  does  not  classify  grappier  cements  obtained  as  by-products  in 
the  manufacture  of  hydraulic  limes,  and  confounds  natural  with  Portland 
cements. 


14  TESTS    OF    CEMENTS. 

which,  the  elements  enter  varies  within  very  wide  limits.  Neither 
can  a  classification  be  based  upon  methods  of  manufacture.  Those 
methods,  for  exactly  those  products  which  it  would  be  most  interest- 
ing to  classify,  are  of  relatively  recent  invention  and  are  continu- 
ally being  modified ;  their  definition,  insufficient  even  at  present, 
would  become  entirely  incomplete  in  the  near  future.  From  the 
commercial  point  of  view  a  classification  would  certainly  have  the 
result  (and  the  observations  exchanged  in  the  committee  have 
abundantly  demonstrated  this)  of  changing  the  name  under  which 
certain  grades  of  cement  are  now  sold.  Such  a  change  would 
introduce  a  great  deal  of  trouble  into  the  manufacture  of  hydraulic 
binding  media,  and  would  give  rise  to  lively  protests. 

For  those  inconveniences,  which  are  real,  will  there  be  found 
sufficient  compensation  in  the  advantages  resulting  from  classify- 
ing the  cements  ?  It  is  doubtful. 

A  more  or  less  exact  definition  of  the  nature  of  various  binding 
media  will  not  prevent  fraud,  notably  the  selling  under  a  certain 
name  of  cements  or  limes  which  do  not  possess  the  corresponding 
qualities  on  which  the  consumer  has  a  right  to  count.  But  when- 
ever there  is  a  real  necessity,  there  should  be  given  the  place  where 
the  product  is  obtained,  and  the  tests  which  the  section  aims  at 
unifying  will  permit  the  completion  and  control  of  the  information 
which  the  manufacturer  should  have  given. 

As  to  those  tests,  after  having  made  a  detailed  study  of  the  sub- 
ject, the  section  has  recognized  that,  in  fact,  it  can  be  proceeded 
with  without  the  materials  tested  having  been  classified  into  any 
definite  category. 

The  methods  recommended  apply  equally  well  to  products  of  all 
kinds,  such  as  Portland  cements,  Roman  cements,  slag  cements, 
grappier  cements,  hydraulic  limes,  etc.,  and  the  slight  modifications 
to  which  those  methods  should  be  subjected,  so  far  as  the  tests 
relating  to  rapid-setting  cements  are  concerned,  can  be  followed 
without  the  absence  of  classification  causing  the  least  trouble  to 
experimenters. 

The  uselessness  of  classification  from  the  point  of  view  of  a  choice 
of  methods  of  tests  has  exerted  a  decisive  influence  on  the  section, 
and  it  has  abstained  from  entering  upon  a  question  which  could 
but  create  in  future  an  obstacle  to  the  adherence  of  a  certain 
number  of  interests  to  the  rules  promulgated  as  the  result  of  its 
studies. 

§  5.  LINE  OF  WORK  ADOPTED  BY  THE  SECTION. 

From  the  preceding  considerations  the  line  of  work  of  the  sec- 
tion has  been  determined.  It  occupied  itself  successively  with 
cements,  limes,  pozzuolana,  santorin  earth,  and  plaster,  which  are 


TESTS   OF   CEMENTS.  15 

the  object  of  five  distinct  parts  of  the  present  report,  the  last  being 
devoted  to  a  recapitulation  of  the  conclusions.  The  methods  of 
testing  materials  now  followed  has  been  examined,  compared,  and, 
where  necessary,  modified  with  a  view  of  obtaining  by  the  simplest 
and  most  practicable  processes  the  most  exact  information.  The 
section  regrets  that  it  has  not  always  arrived  at  a  satisfactory 
solution,  and  has  been  obliged  in  several  cases  to  point  out  the 
defects  in  the  existing  methods,  expressing  the  desire  that  further 
studies  may  permit  them  to  be  perfected.  The  methods  relating 
to  tests,  which,  like  those  of  resistance,  for  example,  furnish  results 
varying  with  the  methods  and  apparatus  adopted,  have  been  defined 
in  the  most  complete  detail.  The  section,  however,  confines  itself 
to  giving  simply  general  instructions  whenever  it  is  a  question  of 
absolute  properties  of  materials,  which,  like  specific  gravity,  remain 
the  same  whatever  method  be  employed  to  determine  them.  In 
summing  the  conclusions  arising  from  a  study  of  the  numerous 
questions  submitted  to  its  examination,  the  section  has  not  lost 
sight  of  the  object  to  be  obtained  as  defined  by  President  Picard  in 
his  discourse  of  December  28,  1891,  "to  advise,  not  to  legislate;  to 
indicate  methods  of  experiment,  not  to  insist  upon  them ;  to  act  by 
persuasion,  by  the  example  of  public  works,  not  by  coercion. "  The 
section  has  sought  to  facilitate  the  means  of  arriving  at  that  end 
by  avoiding  a  disturbance  of  universally-accepted  customs,  the 
injury  of  French  manufactures,  or  of  compromising  the  possibility 
of  a  final  understanding  with  other  nations.  Although  in  execu- 
ting its  mission  it  has  exhausted  all  sources  of  information,  the 
section  is  not  unaware  that  its  conclusions  are  far  from  being  com- 
plete, and  that  there  remains  a  great  deal  to  be  done  to  decide  upon 
certain  and  exact  methods  applicable  to  every  test  relating  to  the 
study  of  masonry  materials. 

Its  efforts,  however,  will  not  have  been  useless  if  it  has  been  able 
to  assist  in  laying  the  foundation  of  a  useful  and  practical  work 
which  can  be  completed  and  made  perfect  in  the  future. 

RECAPITULATION  OF  CONCLUSIONS. 

1.  GENERAL  OBSERVATIONS. 

Although  in  tests  of  masonry  materials  it  is  almost  impossible 
to  determine  results  with  mathematical  exactitude,  it  is  neverthe- 
less useful  to  take  every  precaution  known  in  laboratory  practice, 
that  new  errors  may  not  be  grafted  on  those  which  are  unavoida- 
ble. Such  precautions  are  too  well  known  to  make  it  necessary  to 
mention  them  in  detail  here.  Hence  the  section  confines  itself  to 
presenting  some  observations  relating  to  the  apparatus  to  be 
employed  and  to  the  selection  and  preparation  of  the  test  pieces. 


16  TESTS   OF   CEMENTS. 

There  lias  been  given  in  the  course  of  the  detailed  report  a  com- 
plete description  of  a  certain  number  of  appliances,  and  in  the  case 
of  others  there  have  been  set  forth  the  special  conditions  which 
they  should  fulfill,  having  in  view  the  tests  for  which  they  are 
designed.  It  can  be  added  for  the  latter  that,  in  a  general  manner, 
preference  should  be  given  to  the  simplest  instruments,  those  easi- 
est to  keep  in  repair,  and  those  which  are  best  adapted  to  being 
verified  or  checked.  It  is  indispensable  that  every  instrument 
without  exception  should  be  verified  when  it  is  received,  and  that 
those  should  be  reverified  later  which  become  worn  with  use,  as, 
for  example,  screens  and  briquette  molds,  or  which  have  parts  sus- 
ceptible of  disarrangement  or  deterioration,  such  as  balances  and 
certain  breaking  apparatus.  Concerning  manner  of  taking  and 
preparing  samples,  it  must  not  be  forgotten  that  under  the  influ- 
ence of  humidity  and  carbonic  acid  in  the  air  masonry  materials 
are  subject  to  many  changes  in  their  essential  properties,  some 
among  them  becoming  profoundly  altered.  The  regulations  neces- 
sary to  be  adopted,  in  order  to  avoid  as  far  as  possible  the  causes 
of  error  which  might  result  from  a  defective  manner  of  taking  or 
preparing  samples,  should  evidently  depend  011  the  object  of  the 
tests,  and  vary  as  it  is  a  question,  for  instance,  of  determining  the 
quality  of  cement  that  a  mill  is  manufacturing,  or  of  deciding  upon 
the  receipt  of  a  cargo  of  cement  which  is  required  to  satisfy  cer- 
tain known  conditions.  No  general  law  can  be  formulated  in  this 
respect.  There  are  recapitulated  herein  the  conclusions  arrived  at 
by  the  section  following  upon  a  study  of  the  methods  recommended 
for  tests  of  every  nature  to  which  masonry  materials  should  be 
submitted.  Referring  to  the  detailed  report,  the  section  remarks 
that  those  conclusions  do  not  pretend  to  decide  as  to  the  relative 
value  of  different  tests  for  determining  the  qualities  of  products  and 
the  conditions  of  their  reception. 


CONCLUSIONS  RELATING  TO  TESTS  OF  CEMENTS. 
£  1.  FINENESS  OF  GRINDING. 

The  section  recommends  the  adoption  of  the  following  methods 
for  determining  the  fineness  of  grinding  of  cements. 

(a)  The  sample  will  be  divided  into  four  lots  by  the  aid  of  three 
screens  with  square  meshes,  defined  as  follows : 

(1)  Screen  of  324  meshes  per  square  centimeter,  or  18  threads 
millimeter  in  diameter  per  linear  centimeter. 

(2)  Screen  of  900  meshes  per  square  centimeter,  or  30  threads 
millimeter  in  diameter  per  linear  centimeter. 

(3)  Screen  of  4,900  meshes  per  square  centimeter,  or  70  threads 
yfo-  millimeter  in  diameter  per  linear  centimeter. 

(b)  Tests  will  be  made  on  a  sample  of  100  grams. 

(c)  Screening  by  hand  will  be  considered  finished  when  less  than 
•jV  gram  of  material  will  pass  through  under  the  action  of  25 
movements  of  the  arm. 

(d)  The  use  of  a  shaking  machine  is  recommended  to  eliminate 
rapidly  the  greater  part  of  the  fine  dust. 

(e)  Complete  screening  by  machine  is  also  recommended ;  but  it 
can  not  be  made  the  subject  of  exact  regulation,  since  the  condi- 
tions which  the  machine  should  satisfy  are  not  rigorously  defined. 

(/)  The  results  for  each  screen  will  be  expressed  by  summing 
the  residues  which  do  not  pass  it. 

§  2.  SPECIFIC  GRAVITY. 

As  this  is  a  question  of  an  absolute  quality  of  cements,  the  sec- 
tion does  not  believe  in  recommending  one  apparatus  to  the  exclu- 
sion of  others,  and  confines  itself  to  formulating,  as  follows,  the 
general  arrangements  applicable  to  the  use  of  the  volumenometers : 

(a)  To  determine  the  specific  gravity  of  cements  one  of  the 
methods  actually  in  use  may  be  employed,  provided  it  permits 
obtaining  the  first  decimal  with  certainty  and  the  second  within  an 
approximation  of  two  units. 

(6)  The  precautions  to  be  taken  in  making  the  experiments  are 
the  following : 

(I)  Care  will  be  taken  that  the  cement  is  freshly  pulverized ;  the 
parts  retained  by  a  screen  of  900  square  meshes  per  square  centi- 
meter, as  well  as  those  agglomerated  by  humidity  after  they  have 
been  reduced  to  powder  and  passed  through  a  screen,  will  be  mixed 
intimately  with  the  rest  of  the  sample,  on  the  total  of  which  the 
test  should  be  mad.e, 

15671 2  (17) 


18  TESTS    OF   CEMENTS. 

(2)  The  liquid  to  be  made  use  of  should  be  benzine  or  some 
mineral  oil. 

(3)  The  temperature  should  remain  constant  during  the  entire 
operation,  and  should  not  exceed  15°  C. 

§  3.  APPARENT  DENSITY. 

The  section  recommends  the  adoption  of  the  following  rules : 

(a)  The  apparent  density  of  a  cement  will  be  determined  by 
weighing  a  measure  of  cylindrical  form  10  centimeters  high  and 
having  a  capacity  of  1  liter,  filled  by  means  of  a  sieve  funnel. 

(b)  This  apparatus  is  composed  of  a  vertical  funnel  whose  circu- 
lar section  has  a  diameter  of  2  centimeters  at  the  base  and  15  centi- 
meters at  a  height  of  15  centimeters  above  the  base,  at  which 
height  is  placed  a  perforated  plate  having  per  square  decimeter 
about  1,050  holes  2  millimeters  in  diameter.*     The  funnel  is  pro- 
longed by  a  cylindrical  spout  2  centimeters  in  diameter  and  10 
centimeters  high.     The  apparatus  is  supported  by  a  tripod  frame. 

(c)  The  measure  will  be  placed  5  centimeters  below  the  lower 
extremity  of  the  spout.     The  cement  will  then  be  poured  into  the 
funnel  in  little  masses  of  from  300  to  400  grams,  which  will  be 
forced  to  pass  through  those  screens  by  stirring  with  a  wooden 
spatula  4  centimeters  wide.     The  filling  will  be  stopped  when  the 
base  of  the  cone,  which  will  rise  little  by  little  above  the  measure, 
has  reached  its  upper  edge.     The  excess  of  cement  will  then  be 
scraped  off  by  moving  across  the  top  a  straight  blade  held  in  a 
vertical    plane.     Throughout  the   entire   operation    the    measure 
should  not  be  subjected  to  any  trembling  or  shock. 

(d)  There  will  be  adopted  as  the  weight  of  a  liter  the  mean  of  the 
results  obtained  by  five  successive  measurements. 

(e)  It  is  useful  to  have  the  tests  made  on  the  cement  in  the  con- 
dition it  is  delivered  and  on  the  fine  dust  having  passed  a  screen  of 
4,900  meshes.     In  all  cases  the  degree  of  fineness  of  grinding  of  the 
sample  used  should  be  indicated,  as  well  as  the  apparent  density. 

§  4.  CHEMICAL  ANALYSIS. 

The  conclusions  that  the  section  proposes  to  formulate,  so  far  as 
chemical  analysis  is  concerned,  are  reduced  to  the  following : 

(a)  Operators  should  be  permitted  the  liberty  of  using  any  of 
the  usual  methods  for  determining  the  chemical  composition  of 
cements. 

(b)  Complete  chemical  analyses  are  recommended ;  all  of  the  ele- 
ments found  should  be  indicated,  without  grouping,  in  the  record 
of  proceedings  of  the  operation. 


•  Such  plate  is  found  in  the  market. 


TESTS   OF   CEMENTS.  19 

(e)  In  default  of  a  complete  analysis,  the  mixture  of  the  volatile 
materials  could  furnish  useful  information. 

§  5.  TESTS  OF  HOMOGENEITY. 

A  study  of  the  information  which  may  be  collected  from  the  use 
of  the  magnifying  glass,  in  testing  cements  with  respect  to  homo- 
geneity, has  led  the  section  to  the  following  conclusions : 

(a)  The  magnifying  glass  can  be  employed  usefully  to  give  indi- 
cations of  the  degree  of  homogeneity  of  cements. 

(b)  Observations  should  be  made  on  the  material  retained  by  a 
screen  of  4,900  meshes,  operating  successively  with  magnifying 
powers  of  about  3  diameters  for  the  general  examination  and  of  8 
for  the  detailed  examination. 

(c)  If  the  examination  reveals  the  presence  of  grains  suspected 
of  coming  from  foreign  materials  in  the  cement,  the  nature  of 
those  can  be  verified  either  by  complete  or  by  partial  chemical 
analysis  of  the  entire  product  or  of  the  suspected  portions,  or  by 
any  other  means  that  may  be  judged  most  suitable  to  identify  the 
foreign  materials. 

§6.  MANUFACTURE  OF  STANDARD  PASTES  AND  MORTARS. 

The  section  proposes  to  define,  as  follows,  pastes  and  mortars  on 
which  standard  tests  should  be  made : 

1.  STANDARD  CEMENT  PASTE. 

A.  (a)  To  manufacture  a  standard  paste  1  kilogram  of  cement 
will  be  used,  which  will  be  spread  on  a  marble  table  in  the  shape 
of  a  crown,  in  the  center  of  which  there  will  be  poured  out  at  once 
the  volume  of  water  necessary  to  satisfy  the  following  conditions.  * 

According  to  the  nature  of  the  tests,  fresh  or  sea  water  may  be 
employed. 

The  mixture  should  be  worked  briskly  with  a  trowel  for  five 
minutes,  counting  from  the  moment  when  the  water  was  poured 
out. 

(b)  With  one  portion  of  the  paste  obtained  there  will  be  filled 
immediately  a  flat-bottomed  metallic  box,  truncated  in  form,  hav- 
ing a  diameter  of  8  centimeters  at  the  lower  base,  9  centimeters  at 
the  upper  base,   and   4  centimeters  deep;   the  surface  will  be 
smoothed  off  by  scraping  a  trowel  along  the  upper  surface  of  the 
mold,  avoiding  any  heaping  and  any  shaking. 

(c)  In  the  center  of  the  mass  thus  formed  there  will  be  brought 
down  normal  to  the  surface  of  the  paste,  carefully  and  without 

*  That  volume  ought  to  be  determined  by  means  of  successive  trials. 


20  TESTS   OF   CEMENTS. 

allowing  it  to  acquire  any  velocity,  a  cylindrical  sound  1  centi- 
meter in  diameter  and  weighig  300  grams,  made  of  polished  metal, 
clean  and  dry,  and  terminated  by  a  section  normal  to  the  axis. 

That  apparatus,  called  a  "  consistency  sound,"  should  be  so  con- 
structed as  to  permit  the  exact  determination  of  the  thickness  of 
the  paste  remaining  between  the  bottom  of  the  box  and  the  lower 
extremity  of  the  sound.  Two  tests  will  never  be  made  on  the 
paste  contained  in  the  same  box. 

(d)  The  paste  will  be  considered  standard  whose  consistency  is 
such  that  the  distance  remaining  between  the  bottom  of  the  box 
and  the  end  of  the  sound,  at  the  moment  when  the  latter  ceases  to 
sink  under  the  action  of  its  own  weight,  is  6  millimeters. 

B.  For  rapid-setting  cements  the  quantity  of  cement  used  in  ex- 
periments will  be  reduced  to  500  grams  and  the  duration  of  gauging 
to  1  minute. 

2.  STANDARD  MORTARS. 

A.  (a)  To  manufacture  standard  mortars,  use  will  be  made  of 
the  natural  sand  coming  from  the  shore  of  Leucate  (Aude),  suitably 
screened,  which  will  be  called  standard  sand.     According  to  cir- 
cumstances, either  simple  standard  sand  or  compound  standard 
sand  will  be  used. 

(b)  Simple  standard  sand  will  be  formed  of  grains  passing  a 
plate  screen  perforated  by  holes  1.5  millimeters  in  diameter  and 
retained  on  one  with  holes  I  millimeter  in  diameter. 

(c)  Compound  standard  sand  will  be  formed  by  a  mixture  of 
equal  weights  of  the  following  sands : 

No.  1,  whose  grains,  passing  a  screen  of  2  millimeters,  are  retained 
by  a  screen  of  1.5  millimeters. 

No.  2,  whose  grains,  passing  a  screen  of  1.5  millimeters,  are  re- 
tained by  a  screen  of  1  millimeter. 

No.  3,  whose  grains,  passing  a  screen  of  1  millimeter,  are  retained 
by  a  screen  of  0.5  millimeter. 

B.  (a)  For  tests  other  than  those  of  rupture,  standard  plastic 
mortar  will  be  used,  and  for  rupture  tests  standard  dry  mortar. 

(b)  Standard  mortars  will  be  mixed  in  the  ratio  of  1  part  by 
weight  of  cement  to  3  parts  by  weight  of  sand  and  will  be  gauged, 
according  to  the  nature  of  the  tests,  with  fresh  or  with  sea  water. 

One  kilogram  of  material  (250  grams  of  cement  and  750  grams 
of  sand)  is  mixed  intimately  when  dry;  it  is  then  formed  on  a 
marble  table  in  the  shape  of  a  crown,  in  the  center  of  which  there 
will  be  poured  out  at  one  time  the  quantity  of  water  to  be  employed, 
and  the  mixture  will  be  worked  briskly  with  a  trowel  for  five 
minutes. 


TESTS   OF   CEMENTS.  21 

(c)  For  the  manufacture  of  standard  dry  mortar,  use  will  be 
made  of  simple  standard  sand.     The  quantity  of  water  employed 
in  gauging  will  be  45  grams,  augmented  by  a  sixth  of  that  neces- 
sary to  bring  a  kilogram  of  cement  to  the  state  of  a  standard 
paste. 

(d)  For  the  manufacture  of  standard  plastic  mortar,  use  will  be 
made  of  compound  normal  sand.     The  quantity  of  water  used  in 
gauging  will  be  such  that  the  resulting  mortar  has  a  plastic  con- 
sistency.    To  be  assured  that  this  consistency  is  well  realized,  a 
metallic  box,  designed  for  tests  of  consistency,  will  be  filled  with  a 
part  of  the  mortar  obtained — see  above  §  6,  No.   1,  A  (6) — and 
the  surface  will  be  planed  off  and  smoothed  with  a  trowel ;  the 
consistency  will  be  considered  satisfactory  if,  after  smoothing,  the 
mortar  exudes  a  little  under  the  effect  of  several  blows  of  a  trowel 
struck  on  the  sides  of  the  box. 

C.  For  rapid-setting  cements  the  quantity  of  cement  used  in 
the  experiments  will  be  reduced  to  500  grams  and  the  duration  of 
gauging  to  one  minute. 

D.  It  is  recommended  for  tests  of  mortar,  other  than  standard 
mortars,  that  there  should  be  employed,  in  preference  to  all  others, 
mixtures  of  1  part  by  weight  of  cement  to  2  parts  of  standard 
sand  (rich  mortars)  and  1  part  of  cement  to  5  parts  of  standard 
sand  (poor  mortars).* 

The  first  of  those  mixtures  is  particularly  useful  for  rapid-setting 
cements,  with  a  view  to  completing  the  information  furnished  by 
the  standard  mortars  mixed  1  to  3. 

RECOMMENDATION. — The  section  recommends  that,  after  an  inter- 
national agreement,  standard  plastic  mortars  be  employed  for  tests 
of  every  nature,  to  the  exclusion  of  standard  dry  mortars. 

§  7.  TESTS  OF  SET. 

Under  the  reservations  expressed  below,  the  section  recommends 
the  adoption  of  the  following  rules  for  the  determination  of  set  of 
pastes  and  mortars,  f 

1.  PASTES. 

A.  (a)  In  pastes,  both  the  beginning  and  the  end  of  set  will  be 
determined. 

*  P  being  the  weight  of  water  necessary  to  bring  a  kilogram  of  cement  to  the 
condition  of  standard  paste,  the  weight  of  water  to  employ  should  be  45  grams 
plus  f  of  P  in  the  case  of  a  dry  mortar  mixed  1  to  2,  and  45  grams  plus  £  of  P  in 
the  case  of  a  dry  mortar  mixed  1  to  5,  the  sand  employed  being  always  simple 
standard  sand. 

f  It  is  remembered  that  for  each  one  of  the  tests  concerning  pastes  and  mor- 
tars the  conclusions  relating  to  the  standard  test  (intended  to  characterize  the 
products)  are  stated,  following  those  relating  to  the  corresponding  general  test. 


22  TESTS    OF    CEMENTS. 

(b)  At  the  moment  of  gauging,  the  temperature  of  the  cement, 
the  water,  and  the  air  should  be  comprised  between  15°  and  18°  C. 
Immediately   after  its  mixture,  the  paste,  with  the   precautions 
indicated  hereinbefore  in  §  6  (1,  A),  will  be  introduced  into  a  box 
similar  to  that  described  in  the  same  paragraph  (1,  A  b).     As  soon 
as  it  is  filled  the  box  will  be  immersed  in  a  tank  containing  water, 
and  the  temperature  will  be  kept  between  15°  and  18°  C.     The  box 
will  be  taken  out  of  the  tank  only  for  the  time  necessary  for  each 
determination. 

(c)  For  the  tests  there  will  be  employed  a  metal  needle,  called  the 
Vicat  needle,  which  weighs  300  grams  and  which  is  cylindrical, 
smooth,  clean,  dry,  and  terminated  by  an  end  cut  at  right  angles 
to  the  axis  and  containing  an  area  of  1  square  millimeter  (diameter, 
1.13  millimeters).     The  beginning  of  set  will  be  called  the  instant 
when  the  needle,  descending  normally  to  the  surface  of  the  paste, 
carefully  and  without  being  allowed  to  acquire  any  velocity,  can 
no  longer  penetrate  entirely  to  the  bottom  of  the  box.     The  end 
of  set  will  be  called  the  instant  when  the  surface  of  the  paste  can 
support  the  same  needle  without  penetrating  into  it  any  appreci- 
able distance.     The  corresponding  durations  will  be  counted  from 
the  moment  when  the  gauging  water  has  been  placed  in  contact 
with  the  cement. 

(d)  In  the  case  of  determining  set  in  air,  operations  will  be  con- 
ducted as  has  just  been  indicated,  with  this  difference,  that  the 
box  as  soon  as  it  is  filled  will  be  kept  in  air  at  a  temperature 
between  15°  and  18°  C. ;  care  will  be  taken  to  void  thoroughly  the 
water  as  it  rises  to  the  surface  of  the  paste  and  separates  from  it. 

B.  The  standard  test  of  set  will  be  conducted  on  the  standard 
cement  paste  immersed,  as  has  just  been  described  (A  b). 

2.  MORTARS. 

A.   (a)  In  mortars,  the  end  of  set  only  will  be  determined. 

(b)  At  the  moment  of  tempering  or  gauging,  the  temperature  of 
the  cement,  sand,  and  water  and  the  surrounding  air  should  be 
between  15°  and  18°  C.     Immediately  after  its  manufacture  the 
mortar  will  be  introduced  into  the  box  serving  for  tests  of  con- 
sistency (§  6,  1,  A  b)  and  will  be  struck  and  smoothed.     As  soon 
as  it  is  filled  the  box  will  be  kept  between  15°  and  18°  C.     The  box 
will  be  taken  out  of  the  tank  only  for  the  time  necessary  for  each 
determination. 

(c)  When  it  is  desired  to  determine  the  set  in  air,  operations  will 
be  conducted  as  has  just  been  described,  with  this  difference,  that 
the  box,  as  soon  as  it  is  filled,  will  be  kept  in  air  at  a  temperature 
between  15°  and  18°  C. 


TESTS   OF    CEMENTS.  23 

(d)  The  end  of  set  will  be  determined  by  the  moment  when  the 
surface  of  the  mortar  can  support  without  deformation  the  pres- 
sure of  the  thumb.  The  duration  of  set  will  be  counted  from  the 
moment  when  the  gauging  water  has  been  placed  in  contact  with 
the  mixture  of  sand  and  cement. 

B.  (a)  The  standard  test  of  set  will  be  conducted  on  the  normal 
plastic  mortar  immersed  as  above  described  (A  b). 

(b)  The  end  of  set  will  be  determined  by  the  moment  from  which 
the  consistency  sound  (par.  c,  1,  Ac)  loaded  with  5  kilograms 
brought  down  normal  to  the  surface  of  the  water,  carefully  and 
\vithout  allowing  it  to  acquire  any  velocity,  no  longer  penetrates 
any  appreciable  distance. 

RECOMMENDATIONS. — (a)  The  above  rules  (1  and  2)  apply  to 
rapid-setting  cements  as  well  as  to  slow-setting  cements.  For  the 
first,  at  least,  the  use  of  the  thermometer  ought  to  furnish  useful 
information.  The  section  recommends  that  studies  on  the  subject 
be  continued. 

(b)  The  section  also  recommends  that  the  studies  which  have 
been  undertaken  relative  to  the  set  of  cement  pastes  and  mortars 
be  continued. 

£8.    RUPTURE   TESTS  BY  TENSION. 

The  section  recommends  the  adoption  of  the  following  rules  for 
determining  the  resistances  of  cement  pastes  and  mortars  to 
tension : 

A.  (a)  For  rupture  tests  by  tension,  use  will  be  made  of  bri- 
quettes of  the  form  of  a  figure  8,  called  standard  briquettes, 
having  a  section  in  the  middle  of  5  square  centimeters  and  of  the 
type  of  fig.  1  (p.  24). 

(b)  Molds  presenting  within  the  form  of  the  briquettes  will  be 
placed  on  a  plate  of  marble  or  of  polished  metal  after  having  been, 
as  well  as  the  plate,  well  cleaned  and  rubbed  with  greasy  linen. 
Those  molds  will  be  filled,  six  at  one  time,  from  the  same  gauging, 
in  the  case  of  slow-setting  cements  and  four  at  one  time  in  the  case 
of  rapid-setting  cements,  putting,  at  one  time,  in  each  mold  enough 
material  to  make  it  run  over.  It  will  be  tapped  with  the  finger, 
that  no  voids  be  left,  and  several  blows  with  the  trowel  will  be 
struck  on  the  sides  of  the  molds,  to  complete  filling  and  to  facili- 
tate the  escape  of  air  bubbles.  Then  it  will  be  smoothed  off  by 
passing  the  blade  of  a  straight  knife  almost  horizontally  over  the 
edges  of  the  mold  in  such  a  manner  as  to  take  away  all  the 
excess  without  exerting  any  pressure.  Finally  the  surface  will  be 
smoothed  by  passing  over  it  a  knife  resting  on  its  edge.  If  a 
cement  paste  is  being  operated  upon,  it  must  not  be  taken  out  of 
the  molds  until  it  has  acquired  sufficient  consistency. 


TESTS    OF    CEMENTS. 


(c)  The  briquettes  will  be  taken  out  of  the  molds  by  sliding  the 
molds  on  the  plate,  uiiclamping  them,  and  taking  from  them  the 
briquettes  without  raising  them,  at  the  end  of  twenty-four  hours, 
counting  from  the  beginning  of  gauging,  and  before,  if  necessary, 


in  any  case  where  set  has  certainly  terminated.  In  all  cases,  dur- 
ing this  delay  of  twenty-four  hours,  the  briquettes  should  be  kept 
in  an  atmosphere  saturated  with  humidity,  sheltered  from  air  cur- 
rents and  the  direct  rays  of  the  sun,  at  a  temperature  comprised, 
as  near  as  possible,  between  15°  and  18°  C.  The  delay  of  twenty- 
four  hours  will  be  reduced  to  that  of  one  hour  for  rapid-setting 
cement  pastes  and  to  three  hours  for  mortars  of  the  same  cement. 

(d)  It  is  recommended  to  weigh  the  briquettes  after  taking  them 
out  of  the  molds  if  one  wishes  to  be  assured  of  the  regularity  of 
their  manufacture. 

(e)  At  the  expiration  of  the  delays  fixed  above  in  paragraph  c, 
the  briquettes  will  be  immersed  in  the  medium  chosen  for  their 
storage.     If  the  briquettes  are  immersed  in  fresh  water,  the  depth 
of  water  in  a  tank  should  not  exceed  1  meter,  and  that  water  should 
be  renewed   every  week.     If  they  are  immersed  in  sea  water, 
renewal  should  take  place  every  two  days  during  the  first  week, 


TESTS   OF   CEMENTS. 


25 


and  after  that  every  week.  During  the  first  week,  the  volume 
occupied  by  the  water  in  the  tank  should  be  equal  to  four  times,  at 
least,  that  of  the  briquettes.  In  every  case  the  nature  of  the  stor- 
age water  will  be  specified.  If  the  briquettes  are  preserved  in  air, 
its  hygrometric  state  will  be  kept  as  near  as  possible  to  that  of 
saturation,  and  they  will  be  placed  under  shelter  from  currents  of 
air  and  from  the  direct  rays  of  the  sun.  The  temperature  of  the 
medium  (air  or  water)  will  be  maintained  as  near  as  possible 
between  15°  and  18°  C. 

(/)  The  apparatus  for  rupture  will  be  arranged  in  such  a  way 
that  the  effort  of  tension  exerted  on  the  briquettes  can  be  contin- 
uous, and  increase  at  the  rate  of  5  kilograms  per  second.  The 
form  and  the  method  of  attaching  the  clips  should  conform  to  the 
following  sketch,  which  reproduces  the  arrangement  in  actual  use : 


.  Z 


26  TESTS    OF    CEMENTS. 

(g)  Breaking  will  be  done  at  the  end  of  7  days,  28  days,  3 
months,  6  months,  1  year,  2  years,  etc.,  counting  from  the  gauging. 
It  will  be  done  also  at  the  end  of  twenty-four  hours  for  mortars  of 
rapid-setting  cements,  and  at  the  end  of  from  three  to  twenty-four 
hours  for  cement  pastes  of  that  nature. 

(h)  Briquettes  coming  from  the  same  gauging  will  be  divided  as 
much  as  possible  between  the  different  series  of  six,  which  will  be 
broken  at  the  periods  of  tests  enumerated  in  the  preceding  para- 
graph. The  results  obtained  in  each  test  will  be  rendered  for  each 
one  of  the  six  briquettes ;  their  mean  will  be  formulated,  and  any 
anomalies  will  be  indicated.  The  results  will  be  expressed  by 
saying  that  "the  resistance  to  tension  measured  by  operating  on 
standard  briquettes  in  the  shape  of  a  figure  8,  5  centimeters  square 
in  cross  section,  is  so  many  kilograms  per  square  centimeter." 

B.  (a)  Standard  tests  of  rupture  by  tension  will  take  place  011 
standard  cement  paste  and  on  standard  dry  mortar  preserved  in 
fresh  water.  For  those  tests,  the  general  rules  under  "A"  and  the 
special  rules  hereinafter  will  be  conformed  to  so  far  as  concerns 
the  manufacture  of  briquettes. 

(b)  At  the  moment  of  mixing,  the  cement,  the  sand,  the  air,  and 
the  water  will  be  at  a  temperature  comprised  between  15°  and  18°  C. 
The  standard  dry  mortar  will  be  rammed  into  a  mold  with  a  spat- 
ula of  iron  about  35  centimeters  long,  including  the  handle,  pre- 
senting a  striking  surface  of  25  square  centimeters,  and  weighing 
250  grams.  Quick  little  blows  will  be  given,  first  on  the  circum- 
ference of  the  briquettes,  then  on  the  center;  finally  more  ener- 
getic blows  will  be  given,  following  always  the  same  method  of 
procedure  and  continuing  the  ramming  until  the  mass  commences 
to  have  a  little  elasticity  and  the  water  oozes  to  the  surface.  Cut- 
ting off  and  smoothing  will  then  be  done,  as  has  been  explained 
before  (A  6). 

§9.  RUPTURE  TESTS  BY  COMPRESSION. 

Under  the  reservation  expressed  below,  the  section  recommends 
the  adoption  of  the  following  rules  to  determine  the  resistance  of 
cement  pastes  and  mortars  to  compression. 

A.  (a)  For  rupture  tests  by  compression  there  will  be  taken  as 
briquettes  the  half  briquettes  separated  by  tension.  Each  half 
briquette  will  be  crushed  separately,  but  the  total  will  be  taken  of 
the  results  furnished  by  the  two  half  briquettes.  When  half  bri- 
quettes are  lacking,  use  can  be  made  of  cylindrical  test  pieces  45 
millimeters  in  diameter  and  22  millimeters  high,  made  and  pre- 
served similar  to  the  briquettes  destined  for  tests  of  rupture  by 
tension  (§  8,  A). 


TESTS   OF   CEMENTS.  27 

(6)  Briquettes  which  are  rough  or  present  conspicuous  protuber- 
ances will  be  planed  by  a  light  rubbing  by  hand  on  a  slab  of  grit- 
stone. 

(c)  The  breaking  apparatus  will  be  placed  so  that  the  effort  of 
compression  may  increase  in  a  continuous  manner,  leading  to  the 
crushing  of  a  half  briquette  at  the  end  of  one  or  two  minutes. 

(d)  Tests  will  be  made  at  the  epochs  fixed  for  those  of  rupture 
by  tension,  and  will  take  place,  like  them,  on  a  series  of  six  briquettes. 

(e)  The  results  will  be  rendered  for  each  one  of  the  six  double 
briquettes  (made  up  of  two  twin  briquettes)  submitted  to  the  test. 
At  the  same  time  their  mean  will  be  formulated  and  the  anomalies 
will  be  set  forth.     The  results  will  be  expressed  by  saying  that 
"  the  resistance  to  crushing  measured  by  operating  on  half-standard 
briquettes,  shaped  like  a  figure  8,  is  so  many  kilograms  per  square 
centimeter."* 

B.  The  standard  tests  of  rupture  by  compression  will  take  place 
on  the  standard  briquette  pastes  and  standard  dry  mortars  which 
have  served  in  the  standard  tests  for  rupture  by  tension.     When 
half  briquettes  are  lacking,  cylindrical  test  pieces  45  millimeters  in 
diameter  and  22  millimeters  high,  made  and  kept  in  the  manner 
indicated  for  those  tests,  may  be  employed  (§  8  B). 

C.  For  tests  having  for  their  object  a  comparison  of  mortars 
with  other  materials,  it  is  recommended  provisionally  to  employ  a 
cube  of  50  square  centimeters  face  area,  placed  on  its  side,  f 

In  a  general  way  the  rules  adopted  for  other  materials  will  be 
adhered  to  in  these  tests. 

RECOMMENDATION. — The  section  recommends  that  researches 
should  be  continued  with  a  view  to  studying  the  advantages  which 
might  arise  from  the  use  of  cylinders  of  small  dimensions  for  com- 
pression tests,  as  well  as  the  substitution  of  punching  for  crushing. 

§  10.  RUPTURE  TESTS  BY  BENDING. 

The  section  proposes  to  recommend  rupture  tests  by  flexure, 
which  it  would  be  of  interest  to  introduce  into  current  laboratory 
practice.  The  rules  to  adopt  will  be  the  following : 

A.  (a)  For  rupture  tests  by  flexure,  test  pieces  in  the  form  of 
prisms  12  centimeters  long,  with  a  square  section  of  2  centimeters 
on  a  side,  will  be  employed. 

(b)  The  preceding  directions  as  to  manufacture,  taking  out  of 
molds,  weighing  and  preservation  of  tension-test  briquettes,  as  well 
as  the  periods  of  test,  are  applicable  also  to  flexure  tests. 

*  The  surface  of  a  briquette  (by  which  it  is  necessary  to  divide  the  total  load 
of  rupture)  is  31  square  centimeters. 

f  That  is,  placed  in  such  a  way  that  the  pressure  is  exerted  normal  to  one  of 
the  faces,  which  has  been  in  contact  with  the  sides  of  the  mold. 


28  TESTS    OF    CEMENTS. 

(c)  The  test  piece  to  be  broken  will  rest  on  one  of  its  lateral  faces 
which  has  been  in  contact  with  the  mold,  on  two  knife-edges  dis- 
tant from  each  other  10  centimeters;  the  load  will  be  applied  in  the 
middle  by  the  aid  of  a  slightly-rounded  knife-edge.     The  apparatus 
of  rupture  will  be  placed  in  such  a  way  that  the  force  exerted  on 
the  test  piece  can  increase  in  a  continuous  manner  at  the  rate  of  1 
kilogram  per  second. 

(d)  Results,  as  in  the  case  of  rupture  tests  by  tension  and  by 
compression,  will  be  rendered  for  each  one  of  the  six  test  pieces  sub- 
mitted to  the  tests ;  at  the  same  time  their  mean  will  be  formulated 
and  the  anomalies  presented  indicated.    The  results  will  be  expressed 
by  saying  that  ' '  the  load  of  rupture  by  flexure  is  so  many  kilo- 
grams for  a  prismatic  specimen  with  square  cross  section  of  2  centi- 
meters on  a  side,  placed  on  two  supports,  distant  from  each  other 
10  centimeters." 

B.  Standard  tests  of  rupture  by  flexure  will  be  conducted  on 
pastes  and  mortars  made  and  preserved  as  has  been  indicated  for 
standard  tests  by  tension  (§  8,  B). 

§  11.  DEFORMATION  TESTS. 

Under  the  reservation  expressed  below  concerning  hot  tests,  the 
committee  recommends  the  adoption  of  the  following  rules : 

A.  Tests  intended  to  show  deformations  caused  by  the  presence 
of  expansive  materials  will  be  conducted  on  cement  pastes,  either 
cold  or  hot. 

B.  COLD  TESTS. — (a)    For  those  tests  the  paste  will  be  spread 
out  on  a  glass  plate  in  such  a  manner  as  to  form  a  cake  about  10 
centimeters  in   diameter  and  2  centimeters   thick,  thinning  out 
toward  the  edges.     Immediately  after  their  manufacture,  cakes 
intended  for  tests  in  water  will  be  immersed  in  the  same  condi- 
tions as  the  test  pieces  intended  for  rupture  tests  (§  8,  Ae). 

Cakes  intended  for  air  tests  will  also  be  exposed  under  the  con- 
ditions indicated  for  such  test  pieces  (§  8,  Ae). 

There  will  be  noted  the  condition  of  the  cakes  at  the  ends  of 
periods  of  time  assumed  for  rupture  tests  (7  days,  28  days,  3  months, 
6  months,  1  year,  2  years,  etc.). 

(b)  If  it  is  intended  to  measure  the  swelling  which  is  caused  in 
pastes  of  cement  by  the  effect  of  prolonged  immersion  in  cold  water, 
there  can  be  used  rods  80  centimeters  long,  with  a  square  section 
of  12  millimeters  on  a  side,  which  will  be  placed  vertically  in  glass 
tubes  25  millimeters  in  diameter,  filled  with  water.  The  elonga- 
tion will  be  determined  by  the  displacement  on  a  scale  of  a  needle 
actuated  by  a  stem  which  has  been  sealed  to  the  upper  extremity 
of  the  prism. 


TESTS    OF   CEMENTS.  29 

C.  HOT  TESTS. — (a)  For  those  tests  there  will  be  employed  cyl- 
indrical test  pieces  3  centimeters  in  diameter  and  3  centimeters 
high,  made  in  metal  molds  0.5  millimeter  thick.     Each  mold  will 
be  slit  in  the  direction  of  its  axis  and  will  carry,  soldered  to  each 
side  of  that  slit,  two  needles  15  centimeters  long;  the  increase  in 
the  departure  of  the  extremities  of  those  two  needles  will  measure 
the  swelling. 

(b)  The  molds,  as  soon  as  they  are  filled,  will  be  immersed  in 
cold  water.      As  soon  as   the  set   is  finished,  and  after  a  delay 
which  will  not  exceed  twenty-four  hours  beyond  set,  the  tempera- 
ture of  the  water  will  be  increased  progressively  to  100°  C.,  the 
time  being  comprised  between  one-fourth  and  one-half  hour.     A 
temperature  of  100°  will  be  maintained  for  six  consecutive  hours, 
and  it  will  be  allowed  afterwards  to  cool,  in  order  that  the  final 
measurements  may  be  made. 

(c)  NOTE. — This  method  of  hot  tests  is  not  applicable  to  rapid- 
setting  cements. 

D.  The  standard  tests  of  deformation  will  be  made  on  a  stand- 
ard paste  of  cement. 

RECOMMENDATION. — The  section  recommends  that  prolonged 
experiments  be  made  through  several  years  and  conducted  on  a 
great  number  of  cement  samples,  notably  on  rapid-setting  cements, 
with  a  view  to  furnishing  more  complete  information  than  that 
now  at  hand  concerning  the  comparative  deformation  in  tests  exe- 
cuted hot  or  cold. 

§12.  YIELD  TESTS. 

The  section  recommends  the  adoption  of  the  following  rules : 

A.  (a)  The  yield  of  a  cement  paste  is  the  volume  of  the  paste 
obtained  by  gauging  at  normal  consistency  1  kilogram  of  cement. 
The  yield  in  mortar  of  a  cement  is  the  volume  of  mortar  obtained 
by  gauging  at  a  plastic  consistency  1  kilogram  of  sand  and  cement, 
mixed  in  the  proportions  corresponding  to  that  mortar. 

(6)  The  yield  will  be  determined  by  noting  the  volume  occupied 
in  a  graduated,  cylindrical  glass  test  tube,  about  6  centimeters  in 
diameter,  by  the  paste  of  the  mortar  which  is  introduced  into  it 
immediately  after  gauging,  with  the  precautions  necessary  to  avoid 
as  far  as  possible  the  imprisonment  therein  of  air  bubbles. 

(c)  If  necesary  the  yield  can  be  determined  with  more  precision 
by  molding  the  paste  or  the  mortar  in  a  block  of  any  form  what 
ever  and  determining,  after  hardening,  the  difference  in  weight  in 
air  and  in  water  of  such  a  block  first  dried  from  ooze  water. 

B.  The  standard  test  of  yield  will  be  conducted  on  the  standard 
cement  paste  and  on  the  standard  plastic  mortar. 


30  TESTS    OF    CEMENTS. 

§13.  POROSITY  TESTS. 

While  remarking  that  the  porosity  of  mortars  and  pastes,  although 
capable  of  being  defined  with  precision,  can  not  be  measured  with 
rigorous  exactitude,  the  section  recommends,  concerning  those 
measurements,  the  adoption  of  the  following  rules : 

A.  The  porosity  of  a  paste  or  of  a  mortar  has  for  its  measure 
the  ratio  of  the  volume  of  voids  which  that  paste  or  that  mortar 
presents  to  the  apparent  total  volume,  such  voids  including  the 
volume  occupied  by  the  water  of  absorption  and  by  the  hygrometric 
water,  but  excluding  the  water  of  crystallization  which  evidently 
forms  a  part  of  the  solid.     If  we  call  V  the  apparent  total  volume 
and  v  the  solid  volume,  the  porosity  is  determined  then  by  the 
formula : 

V-v 
Porosity  =      ~~y—' 

B.  (a)  To  determine  the  porosity,  operations  will  be  conducted 
on  specimens  having,  as  far  as  possible,  an  apparent  volume  com- 
prised between  y3^  and  T\  liter. 

(6)  The  solid  volume  (v)  will  be  obtained  by  taking  the  differ- 
ence (P  —  p)  in  the  weight  of  the  dry  test  piece,  weighed  in  air  (P), 
and  the  weight  of  the  test  piece  saturated  with  water  and  weighed 
in  water  (p). 

To  obtain  complete  saturation,  the  test  piece  will  be  kept  for  a 
quarter  of  an  hour  in  air  rarefied  to  a  pressure  not  exceeding  25 
millimeters  of  mercury,  and  the  water  will  be  made  to  arrive  on 
the  test  piece  until  its  complete  immersion  under  the  same  degree 
of  rarefaction.  The  test  piece  once  covered  with  water,  the  atmos- 
pheric pressure  will  be  reestablished,  and  twenty-four  hours  will 
elapse  before  obtaining  the  weight  given  as  p. 

When  convenient  means  for  rarefying  the  air  are  lacking,  complete 
saturation  will  be  produced  by  the  action  of  boiling  water,  when  the 
mortars  can  support  such  action  without  bad  results.  For  that 
purpose  the  test  piece  will  be  allowed  to  remain  in  water  for  forty- 
eight  hours ;  at  the  end  of  that  time  it  will  be  completely  immersed 
in  cold  water,  which  will  be  brought  to  the  boiling  point  and  main- 
tained in  that  condition  for  two  hours.  Then  it  will  be  allowed 
to  cool  without  taking  out  the  test  piece,  and  at  the  end  of  twenty- 
four  hours  will  be  obtained  the  weight  which  is  given  as  p.  To 
dry  the  test  piece  it  will  be  kept,  until  it  no  longer  loses  weight, 
in  a  chamber  heated  to  between  40°  and  50°  C.  The  final 
measured  weight  will  be  P.  For  this  operation  care  will  be  taken 
that  there  does  not  enter  into  the  oven  any  carbonic  acid  coming 
from  the  products  of  combustion  in  the  heating  apparatus.  For 
certain  products,  drying  effected  under  those  conditions  can  not 


TESTS   OF   CEMENTS.  31 

make  all  of  the  hygrometric  water  disappear,  or  may,  on  the  con- 
trary, take  away  a  little  of  the  water  of  crystallization,  which  per- 
mits a  slight  uncertainty  in  the  values  found  for  porosity. 

(c)  The  apparent  volume  of  the  test  piece  (V)  can  be  obtained 
by  direct  measurement,  if  it  presents  a  geometrical  form.  If  not, 
the  volume  will  be  measured  by  taking  the  difference  between  the 
weight  of  the  test  piece  in  water  and  in  air,  its  condition  of  satura- 
tion remaining  the  same.  To  insure  the  constancy  of  that  state  of 
saturation,  the  test  piece  will  be  covered  with  a  thin  layer  of  melted 
grease,  which  will  be  placed  on  with  a  brush  and  spread  out  with 
the  fingers.  Care  will  be  taken  to  weigh  it  in  water  before  it  is 
weighed  in  air. 

C.  (a)  The  standard  test  of  porosity  will  take  place  on  the  stand- 
ard plastic  mortar  twenty-eight  days  old,  preserved  in  water. 

(b)  For  tests  made  on  mortars  of  different  age  and  composition, 
it  is  recommended  to  employ,  preferably,  plastic  mortars  mixed  1 
to  2  and  1  to  5,  and  aged  7  days,  28  days,  6  months,  and  1  year. 

(c)  In  all  cases  there  should  be  indicated  the  composition,  the 
age,  and  the  methods  of  preservation  of  the  mortars  submitted  to 
the  tests. 

§  14.  PERMEABILITY  TESTS. 

The  section  has  not  been  able,  on  account  of  insufficient  informa- 
tion, to  formulate  any  proposition  for  the  measure  of  permeability 
of  pastes  and  mortars  so  far  as  gases  are  concerned.  For  per- 
meability tests  in  the  case  of  water,  the  adoption  of  the  following 
rules  is  recommended : 

A.  (a)  The  permeability  of  pastes  and  mortars  will  be  expressed 
by  the  number  of  liters  of  water  flowing  per  hour  through  a  cubic 
block  50  centimeters  square  on  a  face,  under  the  following  condi- 
tions : 

(b)  The  water  intended  for  filtration  will  be  led  by  a  glass  tube 
35  millimeters  in  diameter  and  11  centimeters  high,  sealed  verti- 
cally by  the  aid  of  pure  cement  to  the  upper  face  of  the  block 
placed  on  its  side,*  which  has  been  previously  scraped  to  remove 
all  foreign  matter.  The  tube,  closed  at  its  upper  end  by  a  rubber 
stopper,  will  be  put  in  communication  with  a  reservoir  elevated  to 
a  level  corresponding  to  the  desired  pressure  of  water. 

There  will  be  adopted  for  this  pressure,  according  to  the  per- 
meability of  the  mortars,  heights  of  10  centimeters,  1  meter,  or  10 
meters,  f 

*  See  footnote  to  §9. 

f  Where  it  is  desirable  to  adopt  different  heights,  multiples  of  \  meter  will  be 
chosen  preferably. 


32  TESTS   OF   CEMENTS. 

(c)  Before  being  submitted  to  the  test  the  block  will  be  immersed 
in  a  tank  during  forty-eight  hours,  with  precautions  necessary  to 
arrive  at  as  complete  saturation  as  possible.     Once  under  test,  the 
block  will  be  kept  immersed  up  to  its  full  height. 

(d)  The  volume  flowing  per  hour  will  be  determined  after  24 
hours,  7  days,  28  days,  3  months,  etc.* 

(e)  The  determination  will  take  place  on  three  similar  blocks ; 
mean  results  will  be  given  corresponding  only  to  the  two  blocks 
that  are  most  concordant.     In  rendering  the  results  for  permea- 
bility at  different  epochs  (24  hours,  7  days,  28  days,  3  months,  etc.) 
there  must  be  given  the  pressure  (TV  meter,  1  meter,  or  10  meters) 
under  which  tests  were  made. 

B.  (a)  The  standard  test  of  permeability  will  take  place  on  the 
standard  plastic  mortar  twenty-eight  days  old,  preserved  in  water. 

(b)  For  tests  made  on  mortars  of  different  age  and  composition 
it  is  recommended  to  employ  preferably  plastic  mortars  mixed  1  to 
2  and  1  to  5,  aged  7  days,  28  days,  3  months,  etc. 

RECOMMENDATION. — The  section  recommends  that  studies  be 
instituted  with  a  view  to  determining  methods  of  testing  for  per- 
meability of  mortars  so  far  as  gases  are  concerned. 

§  15.  TESTS  OF  DECOMPOSITION  BY  SEA  WATER. 

Although  the  conditions  in  which  laboratory  tests  for  decom- 
position of  pastes  or  mortars  by  sea  water  are  made  generally  ex- 
aggerate effects,  such  tests  can  give  useful  indications  and  are 
recommended.  The  section  proposes  to  adopt,  concerning  those 
tests,  the  following  rules : 

A.   (a)  The  tests  will  be  made  by  immersion  and  by  filtration. 

(b)  There  will  be  employed  for  immersion  standard  briquettes 
shaped  like  a  figure  8,  kept  twenty-four  hours  after  their  manu- 
facture in  a  tank  containing   sea  water,  which  will  be  renewed 
every  two  days  for  the  first  week  and  afterwards  every  week. 

During  the  first  week  the  volume  of  water  should  be  equal  to  at 
least  four  times  that  of  the  briquettes. 

(c)  There  will  be  employed  for  filtration  test  pieces  in  the  form 
of  cubical  blocks  similar  to  those  designed  for  permeability  tests, 
arranged  as  has  been  indicated  for  such  tests  (§  14  A).     The  height 
of  pressure  will  be  10  centimeters,  1  meter,  or  10  meters,  according 
to  the  permeability  of  the  specimens  submitted  to  the  tests.     Oper- 
ations will  be  conducted  on  two  series  of  test  pieces ;  those  of  the 
first  series  will  be  kept  in  air,  those  of  the  second  will  be  kept 
immersed  up  to  their  full  height  in  sea  water. 


*At  the  beginning  of  the  tests  the  determinations  will  be  multiplied  if  neces- 
sary. 


TESTS   OF   CEMENTS.  33 

(d)  When  natural  sea  water,  is  lacking  use  can  be  made  of  artifi- 
cial sea  water  having  the  following  composition : 

Grams. 

Sodium  chloride  (NaCl) 30 

Crystallized  sulphate  of  magnesium  (MgOSO3,  7  HO) . .  _  5 

Crystallized  chloride  of  magnesium  (MgCl,  6  HO) 6 

Hydrated  sulphate  of  lime  (CaOSO3,  2  HO) 1. 5 

Bicarbonate  of  potash  (KOHO,  2  CO*) 0. 2 

Distilled  water,  rain  water,  or  boiled  water 1,000 

(e)  Series  of  standard  8-shaped  briquettes  and  cubical  blocks 
will  be  preserved  in  fresh  water  to  serve  for  comparative  tests. 

(/)  The  results  of  the  tests  will  be  expressed  by  giving  the  fol- 
lowing comparative  information  for  the  two  series  of  briquettes : 

(1)  Modification  of  the  appearance  of  the  test  pieces. 

(2)  Resistance  to  tension  and  to  compression  for  the  briquettes 
immersed,  and  to  compression  for  the  blocks  submitted  to  filtra- 
tion. 

(3)  Chemical  composition. 

The  tests  will  be  made,  according  to  circumstances,  after  one  or 
after  several  of  the  periods  fixed  for  resistance  to  rupture  (28  days, 
3  months,  6  months,  1  year,  etc.). 

B.  (a)  The  standard  test  of  decomposition  by  sea  water  will  take 
place  on  the  standard  plastic  mortar;  for  filtration  tests,  operations 
will  be  conducted  on  specimens  twenty-eight  days  old  and  kept  in 
sea  water. 

(&)  For  tests  made  on  mortars  of  different  age  and  composition, 
it  is  recommended  to  use  preferably  mortars  mixed  1  to  2  and  1  to 
5,  aged  7  days,  28  days,  3  months,  etc. 

(c)  In  all  cases  there  will  be  indicated  the  composition,  age,  and 
method  of  preservation  of  the  mortars  submitted  to  the  tests. 

§  16.  TESTS  OF  ADHESION. 

The  section  proposes  to  recommend  for  adhesion  tests  the  adop- 
tion of  the  following  rules,  stating  that  some  among  them  are 
based  upon  a  comparatively  restricted  number  of  experiments 
and  can  not  be  considered  as  definite : 

A.  To  compare  the  adhesive  strength  of  cements  there  will  be 
submitted  to  tests  of  rupture  by  tension  specimens  in  the  form  of  a 
double  T  made  by  the  aid  of  a  special  mold  which  is  designed  as 
shown  in  fig.  3,  each  one  of  the  two  materials  whose  adhesion  is 
studied  constituting  one  of  the  halves  of  each  test  piece. 

For  those  tests,  the  following  rules  will  be  adhered  to : 

B.  STANDARD  TESTS  FOR  COMPARING  THE  ADHESION  OF  DIF- 
FERENT  CEMENTS  TO  THE  SAME  MATERIAL. — (a)  There  will  be 
prepared  standard  adhesion  blocks  of  mortars  composed  by  weight 

15671 3 


TESTS   OF   CEMENTS. 


* 


TESTS   OF   CEMENTS.  35 

of  1  part  Portland  cement,  passing  through  a  screen  composed  of 
900  meshes,  and  2  parts  of  standard  sand  No.  3.  (§  6,  2,  A  c.) 

The  mortar  will  be  gauged  with  9  per  cent  of  water  and  firmly 
compressed  into  a  mold  whose  bottom  is  provided  with  a  movable 
metallic  plate.  The  adhesion  blocks  will  be  immersed  in  fresh 
water  at  the  end  of  twenty-four  hours.  When  it  is  desired  to  use 
them  they  will  be  dried.  Then  the  adhesive  surface  will  be  passed 
over  by  emery  paper. 

(6)  There  will  be  employed  for  this  test  the  standard  plastic 
mortar  which  will  be  introduced  by  a  simple  beating  with  a  trowel 
into  a  mold  placed  in  such  a  way  that  the  standard  adhesive  block 
will  form  the  bottom.  The  taking  of  the  test  piece  out  of  the 
mold  formed  by  the  standard  block  attached  to  the  mortar  to  be 
tested,  will  be  done  as  soon  as  set  has  completely  taken  place. 

(c)  The  rules  for  tension  tests  should  be  followed  as  to  the  num- 
ber and  preservation  of  the  test  pieces,  the  periods  of  test,  the 
mode  of  rupture,  and  the  expression  of  the  results. 

C.  STANDARD  TESTS  FOR  COMPARING  THE  ADHESION  OF  THE 
SAME  CEMENT  TO  DIFFERENT  MATERIALS. — (a)  For  those  tests 
the  above  directions  will  be  followed,  with  this  exception,  that  the 
normal  adhesion  blocks  will  be  replaced  by  blocks  made  of  the 
different  materials  to  be  tested.  If  the  material  can  be  molded 
the  adhesion  block  will  be  made  in  a  mold  like  a  standard  block. 
If  the  material  is  nonplastic  there  will  be  prepared  a  block  several 
millimeters  in  thickness,  having  a  well-smoothed  face,  which  will 
be  placed  at  the  bottom  of  the  mold,  and  the  test  block  will  be 
completed  by  filling  up  the  mold  with  neat  cement. 

(6)  Where  standard  plastic  mortar  is  not  used,  the  composition 
of  the  mortar  employed  will  be  stated. 


THE  INFLUENCE  OF  SEA  WATER 


ON 


HYDRAULIC  MORTARS. 


(37) 


THE  INFLUENCE  OF  SEA  WATER  ON  HYDRAULIC  BINDING  MEDIA.* 
BY  DR.  WILLIAM  MICHAELIS. 


By  allowing  saturated  limewater  to  act  on  the  hydrates  of  silica, 
ferric  oxide,  and  alumina,  there  can  be  obtained  the  following  com- 
pounds of  lime,  representing  the  highest  grades  of  saturation : 

2  SiOf ,  3  CaO  +  x  H2O ; 
2  Fe2O3,  4  CaO  +  y  H2O; 
2  A1,O3,  5  CaO  +  z  H,O. 

The  values  of  x,  y,  and  z  have  not  been  determined  with  certainty ; 
they  are  assumed  by  me  at  6,  7,  and  8,  respectively,  the  minimum 
amount  of  water  being  1  equivalent  of  it  to  1  equivalent  of  CaO. 

Until  it  has  been  demonstrated  with  certainty  that  there  is  a 
difference  between  the  compounds  formed  during  the  action  of 
water  on  calcareous  hydraulic  binding  media  and  those  formed  dur- 
ing the  process  of  hydraulic  set,  it  may  be  assumed  that  during 
set  the  above  enumerated  compounds  are  actually  formed,  and 
that  the  residual  lime  is  eliminated  as  hydrate  of  lime,  a  process 
evidently  taking  place  in  Portland  cement,  in  which,  when  in  its 
hardened  state,  numerous  crystals  of  hydrate  of  lime  are  found 
interspersed. 

As  is  well  known,  H.  Le  Chatelier  assumes  the  following  crys- 
tallizing compounds,  2  CaOSiO2  +  5  H2O,  as  the  hydrosilicate  of 
lime,  and  A12O3,  3  CaO  +  12  H2O  as  the  hydroaluminate  of  lime. 

It  is  of  no  importance  for  the  present  discussion  whether  hydro- 
silicate  of  lime  is  formed  in  crystals  during  hydraulic  set,  or 
whether,  on  account  of  its  absolute  insolubility,  it  can  not  crys- 
tallize, but  is  a  colloid,  f 

It  is  well  known  that  the  compound  A12O3,  3  CaO  expands  con- 
siderably in  absorbing  water.  I  do  not,  therefore,  consider  this 
compound  to  be  a  predominating  one  in  normal  Portland  cements. 

*  An  abstract  of  a  preliminary  article  by  Dr.  Michaelis  on  the  same  subject 
was  published  in  Vol.  CVII,  Minutes  Proceedings  Institution  Civil  Engineers, 
1891.  The  present  article  appeared  in  Verhandlungen  des  Vereines  zur  Befdr- 
derung  des  Gewerbfleisses,  1896. 

Since  the  foregoing  translation  was  sent  to  the  printer,  a  copy  of  a  translation 
into  English,  printed  at  Edinboro,  Scotland,  has  been  received. 

f  Insolubility  in  this  case  means  that  in  the  presence  of  calcareous  earth  silicic 
acid  is  entirely  insoluble  in  water;  hydrosilicate  of  lime,  therefore,  may  be 
decomposed  by  water,  but  is  never  dissolved ;  the  lime  only  passing  into  solution. 

(39) 


40  INFLUENCE    OF    SEA    WATER    ON    HYDRAULIC    MORTARS. 

No  detailed  information  is  given  by  Le  Cnatelier  concerning 
hydroferrate  of  lime,  a  compound,  by  the  way,  which  is  exceed- 
ingly unstable  and  readily  decomposed;  hence  the  existence  of 
none  but  the  first-mentioned  compound  has  been  thoroughly 
demonstrated. 

In  accordance  with  E.  Candlot  I  have  found  the  following  for- 
mula for  the  aluminate  and  sulphate  of  lime  compound :  2  (A12O3, 
3  CaO)  +  5  (CaOSO3)  +  80  H2O  (dried  over  sulphuric  acid) .  Candlot 
gives  120  H2O  for  the  air-dried  crystals.  But  the  combination, 
A12O3,  3  CaO  +  3  CaOS03  +  30  H2O,  has  also  been  observed  by  me.* 

Only  the  second  compound  will  be  considered  here ;  that  is,  the 
one  crystallizing  with  30  equivalents  of  water,  which  is  certainly 
less  than  is  really  the  case. 

Each  part  by  weight  of  aluminate,  which  appears  in  hydraulic 
mortars  in  the  form  of  hydroaluminate  of  lime,  is  able  to  form  12 
parts  by  weight  of  this  double  salt. 

The  hydroferrate  of  lime  behaves  similarly.  I  have  found  its 
formula  to  be  Fe2O.,,  3  CaO  +  2  CaO,  SO3  +  x  HaO,  but  I  have  not 
yet  succeeded  in  obtaining  it  in  crystallized  form.  Being  yet  of 
a  doubtful  character,  this  compound  will  not  be  considered  here 
at  all ;  this  much  may,  however,  be  assumed,  that  it  acts  similarly 
to  the  above-mentioned  double  salt. 

One  part  by  weight  of  A12O3  will  form  3.062  parts  by  weight  of 
2  A1203,  5  CaO  +  8  H2O. 

One  part  by  weight  of  A12O3  will  form  3.7  parts  by  weight  of 
ALA,  3  CaO  +  6  H2O. 

One  part  by  weight  of  A12O3  will  form  4.735  parts  by  weight  of 
A12O3,  3  CaO  +  12  H2O. 

One  part  by  weight  of  A12O3  will  form  11.856  parts  by  weight  of 
sulphate  and  aluminate  of  lime. 

One  part  by  weight  of  A12O3,  3  CaO  +  6  H2O  will  form  3.2175  parts 
by  weight  of  sulphate  and  aluminate  of  lime,  or  4.4636  parts  by 
weight  of  Candlot's  double  salt,  with  120  H2O. 

One  part  by  weight  of  CaO,  SO3  will  form  nearly  3  parts  by  weight 
of  sulphate  and  aluminate  of  lime. 

One  part  by  weight  of  CaO,  H2O  will  form  nearly  2.3243  parts  by 
weight  of  CaO,  SO3  +  2H2O. 

The  true  Roman  cements,  containing  1  part  by  weight  of  sili- 
cate— silicic  acid,  alumina,  ferric  oxide  (manganous  oxide) — to  1.1 
or  1.2  parts  by  weight  of  lime,  are  the  best  hydraulic  mortars 

*The  air-dried  compound,  2  A12O3)  3  CaO  +  5  CaOSO3  +  80  H2O,  when  dried 
over  sulphuric  acid,  has  rendered  22  H2O  [perhaps  2  (A12O3,  3  CaO  +  6  H2O)  + 
5  (CaO,  SO3  +  2  HaO)] ;  dried  at  100°  C.,  it  rendered  16  H2O,  and  heated  to  a  dark 
red,  it  became  anhydrous.  The  anhydrous  double  salt  is  soluble  in  2,214  parts 
by  weight  of  water  at  a  temperature  of  18°  C. 


INFLUENCE    OF    SEA   WATER   OX    HYDRAULIC    MORTARS.          41 

from  a  chemical  point  of  view,  because  on  hardening  they  form 
the  most  stable  compounds,  without  leaving  any  iionsaturated 
residues. 

For  instance,  a  Roman  cement  of  the  following  composition : 

Silicic  acid        =  24.00  per  cent  or,  in  equivalents,  0.400; 

Alumina  =  10.28  per  cent  or,  in  equivalents,  0.200; 

Ferric  oxide       =    4.80  per  cent  or,  in  equivalents,  0.030; 

Lime  =  49.00  per  cent  or,  in  equivalents,  0.875; 

Sulphuric  acid  =    3.20  per  cent  or,  in  equivalents,  0.040; 

Magnesia!         =    5.00  percent; 

Alkali 

Residue  =    3. 72  per  cent; 

100.00  per  cent; 

will  require  0.4  X  f+  0.2  X  f  +  0.03  X  2  -f-  0.04  =  1.2  equivalents  or 
67.2  parts  by  weight  of  lime,  when  the  calcareous  compounds 
mentioned  at  the  opening  of  this  article  are  considered.  As  the 
cement  contains  only  0.875  equivalents  of  lime,  the  formation  of 
compounds  as  rich  in  lime  as  these  is  impossible,  and  compounds 
will  be  formed  that  contain  less  lime  and  are  therefore  more  sta- 
ble: SiO2,  CaO,  2  A12O3,  3  CaO;  2  Fe2O3,  3  CaO.  For  the  forma- 
tion of  these,  only  43.96  parts  by  weight  of  CaO  are  required; 
the  remaining  5.04  parts  of  lime  will  then  enter  into  compounds 
richer  in  lime,  and  no  free  lime  will  remain  after  set. 

A  hydraulic  mortar  composed  as  above  serves  its  purpose  in  the 
best  possible  way.  Leaving  out  of  consideration  for  the  present 
the  double  compound  of  aluminate  and  sulphate  of  lime  A12O3, 
3  CaO  +  3  CaOSO3  +  30  H2O,  it  would  after  set  render  the  follow- 
ing stable  compounds : 

Hydrosilicate  of  lime  with  from  1  to  1. 5  parts  of  CaO  to  1  of  SiO2 ; 

Hydroaluminate  of  lime  with  3  parts  of  CaO  to  2  of  A12O3 ; 

Hydroferrate  of  lime  with  3  CaO  to  2  of  Fe2O8. 

Only  gypsum,  hydrate  of  magnesia,  and  hydrate  of  caustic 
potash  will  form  an  unsaturated  residuum,  the  salts  generated  by 
them  with  sulphuric  acid  being  however  readily  soluble  and  not 
injurious. 

But  as  Roman  cements  are  burnt  at  red  heat,  or  at  moderate  red 
heat  only,  during  which  operation  they  do  not  condense,  they  must 
be  pronounced  from  a  physical  point  of  view  to  be  of  a  porous 
nature ;  the  compounds  forming  during  absorption  of  water  will, 
therefore,  be  contained  in  them  in  a  much  swollen  state;  hence 
the  mortars  produced  with  them  will  shrink  considerably  during 
air  drying,  through  loss  of  loosely-bound  water,  nearly  all  water 
contained  in  these  hydrates,  over  and  above  the  quantity  corre- 
sponding to  the  hydrate  of  lime,  being  such  loosely-bound  water. 


42          INFLUENCE   OF    SEA   WATER   ON   HYDRAULIC  MORTARS. 

Physically  the  hydraulic  limes,  the  best  representative  of  which 
is  lime  of  Theil,  are  quite  close  to  the  Roman  cements.  Their 
density,  at  least  that  of  the  so-called  light  ones,  is  generally  less 
than  that  of  the  Roman  cements. 

Freshly-calcined  lime  of  Theil  contains — 

Silicic  acid  =  22.80  per  cent  or,  in  equivalents,  0.3800; 
Alumina  =  2.57  per  cent  or,  in  equivalents,  0.0250; 

Ferric  oxide  =  0.88  per  cent  or,  in  equivalents,  0.0055; 
Sulphuric  acid  =  0.64  per  cent  or,  in  equivalents,  0.0080; 
Lime  =  68.60  per  cent  or,  in  equivalents,  1.225; 

Magnesia  =    1.60  per  cent. 

The  most  highly  calcareous  compounds  forming  during  set  will 
use  0.38  x|+  0.025X|  +  0.0055X2  +  0.008  =  0.651 5 equivalents,  or 
36.48  parts  by  weight  of  CaO;  consequently  there  remains  an 
unsaturated  residue  of  32.12  parts  by  weight  of  CaO  aside  from 
1.6  parts  by  weight  of  magnesia. 

From  a  physical  point  of  view  Portland  cement  is  much  superior 
to  the  hydraulic  limes,  because  it  acquires  great  density  through 
vitrification  at  white  heat.  During  set  the  pores  are  filled  more 
completely  because,  the  particles  being  closer  together,  there  is  in 
the  same  space  much  more  swelling  substance.  The  mean  pro- 
portion of  mass  in  equal  spaces  is  for  Portland  cement  and  for 
Roman  cement  about  as  5:3,  and  for  Portland  cement  and  hy- 
draulic limes  from  5  : 2.5  to  5  : 2;  vitrified  Portland  cement,  there- 
fore, has  a  much  greater  volume  weight,  and  consequently  its 
mortar  attains  a  much  higher  degree  of  strength  and  density,  or 
rather  of  condensation,  since  Roman  cements  and  hydraulic  limes 
may  likewise  present  a  perfectly  close  grain. 

Chemically,  however,  Portland  cements  are  inferior,  because, 
like  lime  of  Theil,  they  leave  during  hydraulic  set  a  considerable 
residue  of  lime,  striving  for  saturation.  The  following  Portland 
cement,  for  instance,  approaches  the  lower  limit  in  its  percent- 
age of  lime : 

Silicic  acid  —  22.50  per  cent  or,  in  equivalents,  0.3750; 
Alumina  =  8.99  per  cent  or,  in  equivalents,  0.0875; 

Ferric  oxide  =  4.00  per  cent  or,  in  equivalents,  0.0250; 
Sulphuric  acid  =  1.00  per  cent  or,  in  equivalents,  0.0125; 
Lime  =  61.04  per  cent  or,  in  equivalents,  1.0900; 

Magnesia  ) 

A11e  v  =    2.47  per  cent. 

Alkali 


100.00  per  cent. 

The  most  highly  calcareous  compounds  in  this  case  will  require 
0.84375  equivalents,  or  47.25  parts  by  weight  of  lime;  hence  there 


INFLUENCE   OF   SEA   WATER   ON   HYDRAULIC   MORTARS.          48 

will  remain  at  least  13.79  parts  by  weight  of  unsaturated  lime, 
aside  from  magnesia  and  alkali. 

The  following  Portland  cement  approaches  the  upper  limit  in 
its  percentage  of  lime : 

Silicic  acid  =  20.778  per  cent  or,  in  equivalents,  0.3463; 
Alumina  =  5.819  per  cent  or,  in  equivalents,  0.0566; 

Ferric  o±ide  =  2.720  per  cent  or,  in  equivalents,  0.0170; 
Sulphuric  acid  =  0.520  per  cent  or,  in  equivalents,  0.0065; 
Lime  =  68.379  per  cent  or,  in  equivalents,  1.2210; 

Magnesia)        =       m 
Alkali        j 

If  we  assume  the  most  highly  calcareous  compounds  as  having 
actually  formed  during  set  in  this  case,  a  residue  of  29.1  parts  by 
weight  of  unsaturated  lime  will  be  left. 

In  a  Portland  cement  of  average  composition  (1  part  by  weight 
of  silicate  to  2  parts  by  weight  of  lime)  25  per  cent  of  lime,  or  33 
per  cent  of  hydrate  of  lime,  is  thus  separated.  As  for  the  portion 
of  the  hydrate  which  does  not  become  carbonate  of  lime,  it  is 
plainly  discernible  in  all  Portland  cement  mortars  in  a  crystal- 
lized state. 

It  is  readily  understood  that  a  compound  in  which  such  a  con- 
siderable amount  of  caustic  lime  becomes  free  can  not  be  a  chemi- 
cally stable  compound  in  the  beginning.  The  free  lime  will  react 
and  work  until,  in  one  way  or  another,  it  has  entered  into  a  satu- 
rated compound.  At  first,  this  is  done  through  absorption  of  car- 
bonic acid  from  the  surface,  if  the  mortar  is  in  contact  with  air 
or  water  containing  carbonic  acid ;  in  sea  water  the  lime  will  be 
acted  upon  principally  by  the  soluble  compounds  of  sulphuric 
acid.  To  begin  with,  the  completely  free  lime  will  become  car- 
bonate of  calcium  and  sulphate  of  calcium;  after  that  the  lime 
contained  in  the  exceedingly  unstable  ferric-acid  compound  will 
undergo  the  same  change ;  the  aluminate  of  lime  is  then  attacked, 
and  finally  the  silicate. 

The  simple  formation  of  sulphate  of  lime,  with  2  equivalents  of 
water,  implies  a  considerable  increase  of  volume,  and  in  itself  is 
sufficient  to  destroy  the  cohesion  attained  during  the  absorption 
of  water.  But  together  with  this  there  occurs  the  formation  of 
sulphate  and  aluminate  of  lime,  which  implies  an  immense  increase 
of  volume  and  a  consequent  total  destruction  of  all  cohesion ;  this 
double  compound  crystallizes  with  at  least  30,  but  probably  with 
60,  equivalents  of  water,  and  in  doing  so  cleaves  grain  by  grain 
of  the  strongest  mortar  with  irresistible  power,  leaving  merely  an 
incoherent  slime,  in  which  only  such  portions  may  contain  a  cer- 
tain amount  of  cohesion  as  have  been  protected  by  the  formation 
of  carbonate  of  calcium. 


44          INFLUENCE    OF    SEA    WATER    ON    HYDRAULIC    MORTARS. 

On  examining  the  Roman  cements,  the  hydraulic  limes,  and  the 
Portland  cements  in  regard  to  this  formation  of  sulphate  of  lime, 
and  subsequently  of  aluminate  and  sulphate  of  lime,  it  is  found 
that  in  Roman  cements  all  lime  is  bound,  and  has  no  tendency  to 
combine  with  sulphate  of  magnesium.  The  5.44  parts  by  weight 
of  sulphate  of  calcium  present  in  the  mortar,  it  is  true,  are  able 
to  form  at  least  16  parts  by  weight  of  the  double  salt,  that  is,  an 
increase  of  about  11  parts  by  weight  of  solid  substance;  but  it  is 
almost  certain  that  there  is  ample  space  for  this  increase  of  sub- 
stance in  the  pores  of  the  mortar.  According  to  my  observations, 
and  the  experience  of  others,  good  Roman  cements  will  resist  the 
action  of  sea  water  excellently. 

In  lime  of  Theil  the  free  lime  generally  has  been  carbonated  to 
a  great  extent  through  hardening  in  air  before  immersion  in  sea 
water,  and  thereby  is  withdrawn  from  the  possibility  of  forming 
gypsum.  Assuming  that  no  appreciable  formation  of  carbonate 
of  calcium  has  taken  place,  then  about  30  parts  by  weight  of  lime 
would  be  available  for  the  formation  of  gypsum,  and  out  of  39.643 
parts  by  weight  of  hydrate  of  lime,  92.144  parts  by  weight  of  gyp- 
sum might  be  generated,  which  by  itself  would  suffice  to  destroy 
the  mortar;  but,  in  addition  to  this,  the  existing  5.97  parts  by 
weight  of  aluminate  of  lime,  with  a  portion  of  the  gypsum,  would 
form  about  30  parts  by  weight  of  the  double  compound,  making 
an  entire  increase  of  about  60  parts  by  weight  of  solid  substance, 
viz,  30  parts  by  weight  of  the  double  salt  plus  92  parts  by  weight 
of  hydrate  of  lime,  9.25  parts  by  weight  of  hydroaluminate  of 
lime,  and  13  parts  by  weight  of  gypsum  (employed  in  the  forma- 
tion of  the  double  salt). 

In  this  case  the  formation  of  gypsum  plays  the  principal  part ; 
it  alone  renders  an  increase  of  substance  of  52.5  parts  by  weight. 
The  formation  of  the  double  salt  is  comparatively  insignificant, 
hydraulic  limes  containing  little  alumina  and  consisting  mainly  of 
lime  and  silica.  The  double  salt,  however,  undoubtedly  has  a 
much  greater  force  of  crystallization,  consequently  a  greater  force 
of  expansion. 

In  Portland  cements  with  an  average  percentage  of  lime  (64 
per  cent  lime,  7.2  per  cent  alumina,  and  0.8  per  cent  sulphuric 
acid),  there  will  separate,  as  we  saw  above,  about  25  per  cent  of 
CaO  (33  parts  by  weight  of  CaH2O2),  which  will  combine  with 
sulphate  of  magnesium  forming  74.5  parts  by  weight  of  gypsum, 
thus  causing  an  increase  of  substance  of  41.5  parts  by  weight. 
The  existing  7.2  per  cent  of  alumina  had  formed  26.64  parts  by 
weight  of  hydroaluminate  of  lime,  and  now  will  combine  with  the 
existing  gypsum,  forming  at  least  85  parts  by  weight  of  double 
salt.  The  total  increase  of  substance  in  this  case  then  amounts  to 


INFLUENCE   OF   SEA   WATER   ON    HYDRAULIC   MORTARS.          45 

74.5  parts  of  gypsum  plus  85  parts  of  double  salt,  minus  the  exist- 
ing 33  parts  of  CaH2O2,  the  26.64  parts  of  hydroaluminate  of 
lime,  and  36  parts  from  the  existing  gypsum;  that  is,  in  all,  an 
increase  of  64  parts  by  weight.  This  enormous  increase  of  sub- 
stance to  about  125  parts  by  weight  of  water-hardened  mortar 
must  infallibly  cause  its  total  destruction,  unless  the  action  of  the 
soluble  sulphates  upon  each  other  is  prevented  by  especially  favor- 
able circumstances.  Such  circumstances  are  partly  of  a  chemical 
and  partly  of  a  physical  nature. 

Under  ordinary  temperatures  carbonate  of  lime  can  not  be  decom- 
posed by  sulphates ;  hence  the  most  extensive  formation  possible 
of  carbonate  of  calcium  out  of  the  excess  of  hydrate  of  lime  will 
be  the  best  protection.  On  account  of  their  slow  setting,  hydraulic 
limes,  when  used  for  maritime  constructions,  are  allowed  to  harden 
in  air  for  a  long  time  before  being  submerged,  and  in  this  way  are 
enabled  to  absorb  an  abundance  of  carbonic  acid ;  hence,  presum- 
ably, the  fact  that  lime  of  Theil,  for  instance,  has  behaved  much 
better  than  Portland  cement,  which  latter  in  most  cases  succumbs 
to  the  influence  of  sea  water. 

There  are,  therefore,  good  reasons  for  allowing  concrete  blocks 
of  Portland  cement  to  harden  in  air  for  a  long  time  before  sub- 
merging them,  thus  surrounding  them  with  a  protective  shell  in 
which  free  lime  has  changed  into  carbonate  of  calcium.  But  only 
a  layer  of  insignificant  thickness  can  thus  be  saturated  with  car- 
bonic acid  during  a  reasonable  length  of  time,  and  if  the  sea  water 
at  any  subsequent  period  does  penetrate  to  the  core  of  the  block, 
then  the  above-described  chemical  action  and  destruction  will 
occur  after  all,  and  the  outer  shell  of  carbonate  will  be  rent  with 
irresistible  force  and  lifted  off  the  rapidly-decaying  interior. 

Silicate  of  lime  offers  a  fair  resistance  to  the  change  into  car- 
bonate of  lime,  at  least  to  the  total  change.  Carbonic  acid  in  this 
case  behaves  precisely  like  water.  All  lime  beyond  1  equivalent 
is  much  more  soluble  in  water  and  changes  more  readily  into  car- 
bonate of  lime;  the  less  lime  the  more  resistance  the  compound  will 
offer  to  the  attack  of  carbonic  acid.  Even  in  small  briquettes  of 
from  50  to  100  cubic  centimeters,  which  are  kept  in  a  moist  atmos- 
phere of  pure  carbonic  acid,  it  is  very  difficult  to  change  all  lime 
into  carbonate. 

Aluminate  of  lime  decomposes  more-  readily,  and  the  ferrate  of 
lime  is  decomposed  entirely,  by  the  carbonic  acid. 

The  following  investigation  of  the  influence  of  carbonic  acid  on 
the  strength  and  the  resistance  to  sea  water  of  Portland  cement 
mortar  was  made: 

Ten  tensile  briquettes  were  formed  of  1  part  by  weight  of  Stettin 
Portland  cement  (Stern)  and  3  parts  by  weight  of  Berlin  standard 


46 


INFLUENCE   OF   SEA  WATER  ON  HYDRAULIC   MORTARS. 


sand,  and  the  same  number  of  briquettes  of  1  part  by  weight  of 
the  same  cement  and  5  parts  by  weight  of  the  same  sand.  All 
were  allowed  to  harden  in  moist  air  (under  glass  bells)  for  twenty- 
four  hours,  and  after  that  in  hermetically-sealed  bottles  in  distilled 
water  for  fifty-six  days.  Then  half  of  the  test  pieces  were  kept 
under  a  glass  bell  in  moist  carbonic  acid  for  five  weeks,  at  the  end 
of  which  period  they  were  returned  to  those  in  the  bottles  and 
kept  under  water  for  another  four  weeks.  They  were  then  120 
days  old,  and  were  tested  for  tension  as  well  as  compression,  the 
pieces  broken  by  tension  being  held  together  by  rubber  bands  for 
the  crushing  test.  The  results  (strains  given  in  kilograms  per 
square  centimeter)  are  as  follows : 


CEMENT  MOKTAK,  1:3. 

CEMENT  MORTAR,  1:5. 

a.  PROTECTED  AGAINST 
C02. 

b.  TREATED  WITH  C02. 

c.  PROTECTED  AGAINST 
C02. 

d.  TREATED  WITH  C02. 

Tensile 
strength. 

Crushing 
strength. 

Tensile 
strength. 

Crushing 
strength. 

Tensilo 
strength. 

Crushing 
strength. 

Tensile 
Strength. 

Crushing 
strength. 

26.5 

301 

27.5 

336 

13.5 

115 

15.5 

139 

25.5 

323 

30.0 

364 

13.5 

115 

20.0 

150 

28.0 

330 

28.5 

374 

14.0 

96 

16.5 

130 

28.0 

357 

29.0 

322 

14.5 

105 

15.5 

138 

26.0 

237 

27.5 

296 

14.5 

132 

16.5 

133 

26.9 

309 

28.5 

338 

14.0 

112 

16.8 

138 

How  much  of  the  lime  contained  in  the  cement  has  become  car- 
bonate of  calcium  in  the  case  of  b  and  d  ? 

What  was  the  percentage  of  water  in  the  mortars  protected 
against  carbonic  acid,  and  in  those  treated  with  it,  after  drying 
over  sulphuric  acid  ? 

In  regard  to  these  questions  the  following  was  found  for  the 
various  mortars : 

Per  cent. 

(Carbonic  acid 0.565 

t  Water  of  crystallization 3 . 046 

[Carbonic  acid  ..  .  1.506 


Mortar  a.  1 


Mortar  b.  1:3 


Mortar  c.  1:5 


iv/r  ,7    1 


[Water  of  crystallization 3. 150 

[Carbonic  acid 0.483 

t  Water  of  crystallization 2. 336 

(Carbonic  acid 1. 954 

(Water  of  crystallization 1.  896 


The  1:3  mortar  contained  14.383  per  cent  and  the  1:5  mortar 
contained  10  per  cent  of  lime,  consequently  under  b  only  13.3  per 
cent  and  under  d  only  24.86  per  cent  of  the  entire  amount  of  lime 
had  been  carbonated.  It  is,  therefore,  evident  that  the  absorption 
of  carbonic  acid  is  a  very  slow  process,  even  in  such  small  solids  as 


INFLUENCE  OF  SEA  WATER  ON  HYDRAULIC   MORTARS.          47 

tensile  briquettes  (70  cubic  centimeters  with,  a  height  of  23  milli- 
meters), placed  in  a  moist  atmosphere  of  that  gas,  and  that  it 
requires  a  very  long  treatment  to  decompose  the  silicates  and  the 
aluminates  of  lime.  Hence,  even  a  very  long  exposure  of  con- 
crete blocks  in  open  air  can  only  carbonate  them  superficially, 
and  can  not  be  looked  upon  as  a  sufficient  protection  against  the 
destructive  action  of  sea  water. 

Only  after  long  exposure  in  the  powdered  state  to  the  action  of 
carbonic  acid  were  the  entire  contents  of  lime  carbonated ;  this 
shows  that  the  action  of  carbonic  acid  may  be  likened  to  that  of 
fresh  water;  the  less  lime  contained  in  the  hydrosilicates  and 
aluminates  the  greater  their  power  of  resistance. 

Some  of  the  halves  of  the  tensile  briquettes  were  put  into  sea 
water  and  a  2  per  cent  solution  of  sulphate  of  magnesia;  those 
which  had  been  protected  against  absorption  of  carbonic  acid 
decayed  very  rapidly,  but  those  which  had  been  treated  with  car- 
bonic acid  were  also  considerably  affected  after  only  seven  months ; 
the  more  porous  mortars  of  1 :  5  visibly  more,  although  they  had 
absorbed  more  carbonic  acid. 

Hydraulic  mortars  exposed  to  sea  water  should  therefore  consist 
of  the  most  stable  compounds  of  hydrate  of  lime,  with  hydrate  of 
silica,  alumina,  and  ferric  oxide. 

3  3 

2  SiO,  Z  CaO  and  2  A12O3  ^  CaO. 
1  1 

In  fresh  water  the  case  is  much  more  favorable ;  here,  the  free 
lime  only  can  be  either  dissolved  or  carbonated.  The  more  lime 
is  lixiviated  by  water,  the  less  soluble  the  remaining  lime  (which 
is  bound  to  silicic  acid  or  to  alumina)  becomes;  this  has  been 
demonstrated  already  by  Le  Chatelier,  and  my  experiments  on  fully 
hardened,  neat  Portland  cement  have  verified  it.  The  mortar  may 
have  become  more  porous,  but  complete  dissolving  of  all  of  the 
lime  will  hardly  ever  occur.  On  a  small  scale  Portland  cement, 
which  has  been  protected  against  absorption  of  carbonic  acid,  may 
be  completely  freed  of  its  lime  by  digestion  with  boiled  distilled 
water,  leaving  only  the  hydrates  of  silica,  alumina,  and  ferric  oxide. 
But  pieces  of  only  a  few  cubic  centimeters  volume  require  a  treat- 
ment of  years  with  very  large  volumes  of  water,  in  order  to  effect 
perfect  decomposition. 

In  fresh  water,  therefore,  the  exact  opposite  of  the  above  process 
takes  place;  the  lime  partly  exudes  from  the  mortar  and  thus 
leaves  it,  it  is  true,  in  a  more  porous  state,  but  in  a  faultlessly- 
made  cement  there  will  never  develop  strains  which  destroy  the 
cohesion  of  the  mass.  If  Portland  cement  containing  up  to  70  per 
cent  of  CaO  hardens  with  water,  then  the  binding  force  during 


48          INFLUENCE   OF   SEA   WATER   ON    HYDRAULIC    MORTARS. 

the  formation  of  hydrates  is  greater  than  the  expansive  force  of 
swelling  if  the  separation  of  lime  takes  place  uniformly  through- 
out the  entire  mass.  Here  the  increase  in  volume  of  lime  is  incon- 
siderable, as  in  caustic  lime  which  has  been  mixed  dry  with  sand  and 
then  gauged  with  water.  The  increase  in  volume  in  these  cases  ap- 
pears to  take  place  in  the  pores,  thus  causing  the  mass  to  increase  in 
density.  The  matter  is  different  when  imperfect  physical  mixtures 
are  burned ;  then  the  vitrified  cement  contains  free  lime  (coarse 
grains  in  the  interior),  also  silicates,  aluminates,  and  ferrates  of  too 
highly  calcareous  a  nature,  of  which  those  with  3  equivalents  and 
more  of  CaO  to  1  equivalent  of  SiO2,  A12O3,  and  Fe2O3  will  show 
during  the  absorption  of  water  an  increase  of  volume  similar  to  that 
of  free  lime.  At  any  rate  I  have  demonstrated  by  means  of  melted 
Portland  cement  that  there  is  a  Portland  cement  entirely  constant 
in  volume,  consisting  of  1  part  by  weight  of  silicate  (silica, 
alumina,  ferric  oxide  (manganese))  to  2.4  parts  by  weight  of  lime, 
or,  according  to  French  designation,  with  a  factor  of  hydraulicity 
of  0.416. 

It  is  evident  that  closeness  of  grain — in  other  words,  impervious- 
ness — is  a  very  important  consideration. 

Magnesia,  which  forms  during  the  action  of  sea  water  on 
hydraulic  mortars,  and  which  has  erroneously  been  accused  of 
causing  their  destruction,  so  far  from  doing  this  is  really  a  protec- 
tion, since  under  the  action  of  hydrate  of  lime  on  sulphate  of  mag- 
nesia the  insoluble  hydrate  of  magnesia  will  form  and  aid  in  closing 
pores,  that  is,  in  increasing  imperviousness. 

The  injurious  influence  of  sea  water  should  no  longer  be  attrib- 
uted to  the  salts  of  magnesia,  since  such  injury  results  only  from 
the  sulphuric  acid  or  from  the  soluble  sulphates  in  the  sea  water. 
Sulphate  of  magnesia,  it  is  true,  is  the  special  sulphate  active  in 
sea  water,  but  sulphate  of  calcium,  sulphate  of  any  alkali — in  short, 
every  sulphate  soluble  in  water — has  precisely  the  same  character 
of  destructive  influence,  although  not  the  same  amount  of  energy. 

Other  mechanical  means  of  protection  consist  in  incrustations  of 
vegetation  and  animals  or  in  layers  of  mud  covering  the  surface 
and  preventing  permanent  action  of  sea  water. 

Not  considering  physical  qualities,  it  has  been  demonstrated 
through  my  investigations  that  the  most  highly  calcareous 
hydraulic  binding  media  offer  the  least  resistance  to  the  action  of 
sea  water,  and  that  it  is,  therefore,  a  great  mistake  to  add  lime  to 
such  mortars.  The  fact  that  mortars  of  Portland  cement  and  of 
hydraulic  lime  do  not  keep  nearly  as  well  as  those  of  Roman 
cements  is  proof  sufficient  that  free  lime  is  the  principal  cause  of  their 
destruction  by  sea  water.  The  higher  the  percentage  of  lime  in 
Portland  cement,  the  more  hydrate  of  lime  remains  free  and  striv- 
ing for  saturation  and  the  greater  is  the  increase  of  volume  through 


INFLUENCE    OF   SEA   WATER    OX    HYDRAULIC    MORTARS.          49 

formation  of  gypsum;  hence  the  fact  that  modern  Portland 
cements  of  great  strength  are  found  less  suitable  for  maritime  con- 
structions than  the  older,  less  calcareous  ones.  The  cement  quoted 
as  an  example  above,  in  which  the  percentage  of  lime  is  nearly  the 
practically  possible  maximum,  would  suffer  a  greater  increase  of 
volume  (70  parts  by  weight  to  125)  if  all  separated  lime  were  to 
change  into  sulphate  of  calcium  and  all  hydroaluniinate  of  lime 
into  the  double  compound  of  aluminate  and  sulphate  of  lime  with 
only  30  equivalents  of  water,  although  in  this  case  the  amount  of 
the  double  salt  formed  would  be  less. 

Hydraulic  mortars  with  free  caustic  lime  possess  just  as  little 
stability  physically  as  they  do  chemically.  Absorption  of  water, 
even  if  it  is  only  of  a  hygroscopic  nature,  causes  swelling,  and 
consequently  strong  pressure  strains  as  well  as  molecular  changes. 
To  begin  with,  alkali  becomes  free  and  energetically  absorbs  water 
and  carbonic  acid,  the  latter  soon  combining  with  the  hydrate  of 
lime.  As  is  well  known,  caustic  lime  can  absorb  carbonic  acid  in 
the  presence  of  free  water ;  dry  carbonic  acid  does  not  act  upon 
dry  hydrate  of  lime.  But  during  each  drying  the  higher  hydrates 
will  lose  water,  tensile  strains  will  develop,  and  shrinking  and 
cracking  will  occur.  Lime  surely  does  not  form  one  hydrate  only, 
but  hydrates  may  be  assumed  with  5  and  8  equivalents  of  water, 
although  it  may  be  difficult  to  demonstrate  their  existence  with 
certainty.  Undoubtedly  there  is  a  gelatinous  hydrate  of  lime,  for 
which,  through  separation  with  absolute  alcohol,  I  have  found  the 
formula  CaO  +  5  H2O,  which  seems  to  indicate  the  existence  of 
a  still  higher  hydrate. 

In  this  way  cement  mortar  will  continue  for  years  to  expand,  to 
crack,  and  to  destroy  itself,  each  absorption  of  water  causing 
expansion,  each  drying  out  shrinkage ;  each  absorption  of  carbonic 
acid  causing  either  expansion  or  shrinkage,  according  to  whether 
simple  or  higher  hydrates  are  changed ;  and  a  substance  as  inelastic 
as  cement  mortar  can  not,  as  a  rule,  resist  for  any  length  of  time 
the  influence  of  such  occurrences.  All  these  drawbacks  will  clearly 
be  lessened  if  the  caustic  lime  remaining  or  becoming  free  during 
set  can  be  bound  by  giving  it  a  chance  to  form  stable  hydro-com- 
pounds with  hydraulic  silica  and  alumina. 

It  is  true  that  the  lixiviation  of  the  caustic  alkalis  can  not  be  pre- 
vented in  this  way,  but  on  account  of  their  small  amount  and  their 
ready  solubility  they  are  not  of  great  importance  and  certainly  do 
not  endanger  the  permanence  of  the  mortar.  In  water  they  are 
simply  washed  out,  and  when  hardening  takes  place  in  air  they 
are  a  disfigurement  more  than  anything  else,  and  besides  a  tem- 
porary one  only,  since,  unlike  the  exudations  of  lime,  they  can  be 
removed  by  washing  with  water. 

15671 4 


50  INFLUENCE    OF    SEA   WATER   ON    HYDRAULIC    MORTARS. 

It  is  clear  now  that  110  greater  mistake  could  be  made  than  add- 
ing lime  paste  to  hydraulic  binding  media,  which  already  contain 
an  excess  of  lime,  that  is,  to  Portland  cement  mortars;  their 
destruction  is  simply  hastened  in  this  way.  My  investigations 
demonstrated  clearly  that  even  in  mortars  exposed  to  fresh  water 
the  results  of  this  proceeding  are  only  apparently  favorable,  while 
in  reality  they  are  injurious;  the  excess  of  lime  dissolves  rather 
easily,  and  its  washing  out  leaves  the  mortar  more  porous  and 
therefore  more  susceptible  to  disintegration.  After  two  or  three 
years  a  considerable  diminution  of  strength  becomes  apparent  in 
such  cement-lime  mortars.  Frequently,  it  is  true,  carbonic  acid 
may  exercise  a  favorable  influence ;  but  I  demonstrated  long  ago 
that  this  proceeding  is  justified  only  in  the  case  of  poor  mortars 
exposed  to  air,  in  order  to  increase  their  plasticity. 

In  No.  33,  1882,  'of  the  "Deutsche  Topfer  und  Ziegler  Zeitung," 
I  discussed  the  question  of  the  excess  of  lime  in  cement  as  fol- 
lows: 

When  Portland  cement  is  tempered  with  water  there  undoubtedly  takes  place 
during  set  a  shifting  of  molecules  simultaneously  with  and  in  consequence  of  the 
absorption  of  water.  In  the  alkaline  waters  thus  forming  in  the  cement  about 
one -third  of  the  existing  lime  separates  in  crystals  of  hydrate  of  lime  during  the 
the  process  of  hardening.  This  crystalline  lime,  instead  of  having  any  binding 
power,  has  rather  a  tendency  to  destroy  the  cohesion  obtained;  but  in  good 
cements  this  tendency  will  not  be  realized,  because  the  very  gradual  separation 
of  lime  finds  cohesion  too  much  advanced. 

Considering  this  state  of  affairs,  we  may  a  priori  infer  that  the  quantity  of 
actual  cement  in  the  mortar  can  be  increased  by  an  addition  of  pozzuolana ;  that 
is,  a  substance  with  which  hydrate  of  lime  will  combine  to  form  cement ;  in  this 
way  the  crystallizing  of  caustic  lime  can  be  prevented  altogether,  all  hydrate  of 
lime,  as  it  becomes  free  and  before  it  has  crystallized  from  the  solution,  being 
employed  in  forming  hydrosilicate  or  hydroaluminate  of  lime. 

The  "German  Union  of  Cement  Manufacturers"  in  1882  opposed 
this  view  in  the  following  words : 

Standard  Portland  cements  do  not  stand  in  need  of  any  so-called  improving 
admixture ;  such  admixtures  cause  a  decrease  of  strength  almost  proportional 
to  their  quantity. 

In  a  published  communication  to  the  "Union,"  1884,  I  again 
demonstrated  the  correctness  of  my  theoretical  deductions  concern- 
ing hardening  in  fresh  water. 

The  Royal  testing  station  for  binding  media  in  Berlin  has  not  been 
able  to  elicit  any  thing  but  the  absolute  confirmation  of  my  assertions, 
and  Professor  L.  von  Tetmajer  published  in  the  "  Schweizerische 
Banzeitung,"  No.  24,  1884,  his  observations  on  the  action  of  some 
admixtures  on  Portland  cement,  showing  an  actual  increase  of 
tensile  and  crushing  strength,  although  the  density  of  such  admix- 
tures was  much  less  than  that  of  Portland  cement.  The  improve- 


INFLUENCE   OF   SEA   WATER   ON   HYDRAULIC   MORTARS.          51 

ment  of  Portland  cement  by  means  of  suitable  admixtures  was 
thus  clearly  demonstrated.* 

The  study  of  the  behavior  of  hydraulic  mortars  in  sea  water 
having  convinced  me  that  the  principal  cause  of  their  frequent 
failure  is  to  be  sought  in  the  presence  of  free  lime,  it  seemed  clear 
that  such  mortars  could  be  improved  by  admixtures  containing 
hydraulic  silica.  By  means  of  such  suitable  admixtures  the  entire 
excess  of  lime  could  be  bound  and  the  mortar  thus  made  very  much 
less  susceptible  to  decomposition.  Aside  from  permanence,  it 
seemed  certain  that  this  would  very  soon  and  unmistakably  find 
expression  in  the  strength  of  the  mortar,  consequently  the  behavior 
of  mixed  hydraulic  binding  media  in  sea  water  was  necessarily  the 
most  rigid  criterion  of  my  theory.  I  was  thus  induced  to  formu- 
late a  method  of  test  for  that  purpose. 

The  action  of  sea  water  on  these  binding  media  is  principally  a 
chemical  one,  and  in  order  to  obtain  early  results  in  this  direction 
it  was  necessary  to  exclude  everything  impeding  such  action.  It 
would  have  been  a  mistake  to  experiment  with  impervious  mortars, 
or  with  mortars  protected  by  an  outer  shell  through  absorption  of 
carbonic  acid;  the  object  in  view  demanded  rather  the  selection 
of  porous  mortars,  in  which  the  action  of  the  sea  water  would  meet 
with  no  obstruction. 

The  following  solutions  were  employed  for  my  experiments : 

(1)  Artificial  sea  water,  composed  as  follows : 

Kitchen  salt.. grams.  30 

Sulphate  of  magnesium do_.  12 

Chloride  of  magnesium.-- do__  3 

Sulphate  of  calcium do  .  _  1 

Water liter.  1 

Alkaline  carbonate  was  left  out  purposely,  there  being  no  object 
in  weakening  the  action  of  the  sea  water.  In  order  to  keep  the  per- 
centage of  sulphuric  acid  constant,  cylinders  of  gypsum  wrapped 
in  linen  were  suspended  in  the  water.  The  latter  was  renewed 
daily  in  the  beginning,  after  that  weekly,  and  at  the  end  of  three 
months  monthly ;  it  was  thoroughly  stirred  every  day. 

(2)  Saturated  solution  of  sulphate  of  calcium  with  cylinder  of 
gypsum  suspended  in  it. 

(3)  One  per  cent  solution  of  crystallized  sulphate  of  magnesium. 

(4)  Two  per  cent  solution  of  crystallized  sulphate  of  magnesium. 

(5)  Three  per  cent  solution  of  crystallized  sulphate  of  magnesium. 

(6)  One  and  three-tenths  per  cent  solution  of  crystallized  sul- 
phate of  soda. 

*See  Zum  Dogma,  etc.,  1884;  again  E.  Dietrich  Wochenblatt  fur  Baukunde,. 
1885,  Nos.  93  and  95,  W.  Michaelis,  ibidem,  1888,  No.  43. 


52          INFLUENCE   OF    SEA   WATER   ON   HYDRAULIC   MORTARS. 

L.  Vicat  had  already  employed  a  solution  of  sulphate  of  soda, 
and  had  recognized  its  destructive  nature  on  hydraulic  binding 
media. 

Fifteen  years  ago  I  found  that  a  solution  of  sulphate  of  calcium 
with  only  0.127  per  cent  of  sulphuric  acid  (SO3)  will  completely 
destroy  neat  Portland  cement.  I  then  perceived  that  only  sulphuric 
acid  acts  destructively  on  hydraulic  binding  media  exposed  to  sea 
water,  and  that  magnesia  is  simply  one  of  the  visible  symptoms 
of  such  destruction,  which,  far  from  being  injurious,  rather  causes 
a  favorable  influence  by  closing  the  pores,  thus  restricting  destruc- 
tion to  its  beginning. 

Still,  it  is  readily  understood  why  the  action  of  sulphate  of  mag- 
nesium must  be  a  much  more  energetic  one  than  that  of  sulphate 
of  calcium;  the  latter  can  only  cause  the  formation  of  the  double 
compound  sulphate  and  aluminate  of  lime,  while  the  former,  besides 
this,  will  change  the  free  and  loosely-bound  lime  with  which  it  comes 
in  contact  into  gypsum.  The  enormous  expansion  and  destruction 
often  seen  in  cement  mortar  exposed  to  sea  water  can  be  understood 
when  we  remember  that  at  least  one-third  of  the  cement  changes 
into  sulphate  of  calcium  with  2  equivalents  of  water. 

Portland  cements  rich  in  alumina  are  especially  susceptible  to 
decomposition  by  a  solution  of  sulphate  of  calcium,  and  most  mari- 
time structures  built  with  these  binding  media  have  been  saved 
from  complete  and  early  ruin  merely  through  such  favorable  cir- 
cumstances as  impermeability,  absorption  of  carbonic  acid,  incrusta- 
tion, closing  of  pores,  etc. 

I  will  now  proceed  to  render  an  account  of  the  experiments  made 
to  support  my  assertions.  In  the  main  these  experiments  consisted 
of  two  series,  one  of  which  has  been  completed,  the  other  com- 
menced. The  first  series  consisted  principally  of  rich  mortars,  viz, 
1 : 2.5  and  1:4;  the  second  series  consisted  of  porous  mortars,  prin- 
cipally in  the  proportion  of  1:5. 

For  the  first  series,  Bauschinger  bars  of  5  square  centimeters 
cross  section  and  a  length  of  10  centimeters  were  made,  the  sand 
used  being,  where  not  otherwise  stated,  quartz  sand  of  mixed  grain, 
and  the  trass  being  Rhenish  trass  from  the  Nette  valley.  The 
mortar  was  gauged  in  the  following  proportions  by  weight : 

(1)  Four  of  Portland  cement  (Stern  brand)  containing  less  than 
6  per  cent  alumina  and  10  of  quartz  sand. 

(2)  Two  of  same  cement,  2  of  trass,  and  10  of  quartz  sand. 

(3)  Four  of  same  cement,  1.2  of  hydrate  of  silica  (air-dried),  and 
13  of  quartz  sand. 

(4)  Four  of  same  cement,  1.1  of  kaolin  from  Zettlitz  baked  at 
red  heat,  and  12.7  of  quartz  sand. 


INFLUENCE   OF   SEA    WATER   ON    HYDRAULIC   MORTARS.          53 

(5)  Four  of  Portland  cement,  containing  about  9  per  cent  alu- 
mina (raw  material  washed),  and  10  of  quartz  sand. 

(6)  Two  of  same  cement,  2  of  trass,  and  10  of  quartz  sand. 

(7)  Four  of  same  cement  and  16  of  standard  sand. 

(8)  Four  of  same  cement,  1.2  of  hydrate  of  silica  (air-dried),  and 
13  of  quartz  sand. 

(9)  Four  of  same  cement,  1.1  of  kaolin  from  Zettlitz  baked  at 
red  heat,  and  12.7  of  quartz  sand. 

(10)  Four  of  Portland  cement,  containing  about  9  per  cent  alu- 
mina (worked  dry),  and  10  of  quartz  sand. 

(11)  Two  of  same  cement,  2  of  trass,  and  10  of  quartz  sand. 

(12)  Four  of  same  cement  and  16  of  standard  sand. 

(13)  Four  of  same  cement,  1.2  of  hydrate  of  silica  (air-dried), 
and  13  of  quartz  sand. 

(14)  Four  of  same  cement,  1.1  of  kaolin  from  Zettlitz  baked  at 
red  heat,  and  12.7  of  quartz  sand. 

(15)  One  hundred  of  Bavarian  Roman  cement  and  36  of  water. 

(16)  Four  of  same  Roman  cement  and  10  of  quartz  sand;  13  of 
water. 

(17)  One  hundred  of  Bosnian  Roman  cement  and  36  of  water. 

(18)  Four  of  same  Roman  cement  and  10  of  quartz  sand;  13  of 
water. 

(19)  Four  of  lime  of  Theil  and  12  of  standard  sand. 

(20)  Four  of  lime  of  Theil  and  20  of  standard  sand. 

(21)  Five  of  hydrate  of  silica  (air-dried),  12.5  of  paste  of  marble- 
lime  (32  per  cent  residuum  after  calcination),  and  20  of  quartz 
sand. 

(22)  Six  of  kaolin  from  Zettlitz  baked  at  red  heat,  16.5  of  paste 
of  marble-lime  (32  per  cent  residuum  after  calcination),  and  28.5 
of  quartz  sand. 

(23)  Four  of  anhydrite  of  silica  and  19  of  paste  of  marble-lime 
(32  per  cent  residuum  after  calcination). 

All  bars  made  from  these  mortars  were  allowed  to  harden  in 
moist  air,  but  protected  against  carbonic  acid ;  after  that,  half  of 
the  bars  were  exposed  in  hermetically-sealed  bottles  to  a  solution 
of  gypsum  kept  in  a  state  of  saturation,  and  the  other  half  exposed 
in  the  same  manner  to  a  1  per  cent  solution  of  sulphate  of  mag- 
nesium. 

The  solution  was  renewed  daily  during  the  first  two  weeks,  then 
weekly,  and  at  the  expiration  of  three  months  monthly. 


54 


INFLUENCE   OF   SEA   WATER   ON   HYDRAULIC   MORTARS. 


The  following  observations  were  made  on  the  bars  exposed  to 
the  solution  of  gypsum : 


Mortar  No. 

Commencement  of  destruction. 

Total  destruction. 

1 

After  6  months. 

After  1  year. 

5 

After  6  months 

After  1  year. 

7 

After  3  months 

After  6  months. 

10 

After  3  months 

After  9  months. 

12 

After  3  months 

After  6  months. 

20 

After  1  year 

22 

After  14  days 

After  1  month. 

All  others  are  intact  at  this  date,  that  is,  after  a  lapse  of  two 
years. 

The  following  observations  were  made  on  the  bars  exposed  to  a 
1  per  cent  solution  of  sulphate  of  magnesium : 


Mortar  No. 

Commencement  of  destruction. 

Total  destruction. 

1 

After  6  months 

After  1  year. 

5 

After  6  months 

After  9  months. 

7 

After  4  months 

After  6  months. 

10 

After  3  months 

After  9  months. 

12 

After  3  months 

After  6  months. 

17.. 

After  18  months  . 

20  . 

After  12  months 

22 

After  8  days 

After  1  month. 

These  tests  demonstrate  that  mortar  No.  22,  consisting  of  kaolin 
and  paste  of  lime,  is  rapidly  destroyed  in  a  solution  of  gypsum,  as 
well  as  in  one  of  sulphate  of  magnesium,  while  the  same  mortar 
remained  perfectly  sound  during  exposure  to  fresh  water.  There 
are  two  reasons  for  this :  In  the  first  place,  kaolin  baked  at  red 
heat  is  a  very  porous  pozzuolana,  and  therefore  renders  a  mortar 
of  little  density;  in  the  second  place,  kaolin  is  richer  in  alumina 
than  any  other  pozzuolana,  being  composed  of  55  per  cent  of  silica 
to  42  per  cent  of  alumina. 

Mortar  No.  22,  therefore,  was  composed  as  follows : 

3. 30  parts  by  weight  of  silica  or,  in  equivalents,  550 ; 

2.52  parts  by  weight  of  alumina  or,  in  equivalents,  244; 

5.28  parts  by  weight  of  lime  or,  in  equivalents,  943. 

It  is  seen  that  the  almost  exact  formation  of  SiO2  CaO  -f-  A12O3, 
3  CaO  is  possible  here ;  the  aluminate  is  the  sole  cause  of  destruc- 
tion, and  the  rapidity  of  the  latter  is  due  to  the  high  percentage  of 
alumina.  We  have  seen  above  that  1  part  by  weight  of  alumina 
can  form  nearly  12  times  as  much  of  aluminate  and  sulphate  of 
lime  by  combining  with  3C  equivalents  of  water ;  now  mortar  No. 


INFLUENCE   OF   SEA   WATER   OX   HYDRAULIC   MORTARS. 


00 


22  contains  22.7  per  cent  of  alumina,  consequently  270  parts  by 
weight  of  the  double  compound  may  be  found  in  it. 

Notwithstanding  this,  the  three  Portland  cement  mortars  mixed 
with  kaolin  have  stood  well  so  far  (for  2  years),  doubtless  owing 
to  the  combining  of  the  free  lime  with  the  admixture. 

The  unmixed  Portland  cements  have  decayed  rapidly ;  those  with 
9  per  cent  of  alumina,  in  accordance  with  theory,  sooner  than  the 
Stern  cement  (containing  only  5  to  6  per  cent).  The  lime  of  Theil 
has  stood  so  far;  the  porous  mortar  of  1 : 5,  the  hardening  of  which 
took  place  under  exclusion  of  carbonic  acid,  shows  commencement 
of  destruction  at  the  most  sensitive  part  of  one  bar,  viz,  the  edge. 

The  Bavarian  Roman  cement,  both  neat  and  mixed  with  quartz 
sand  in  the  ratio  of  1:2.5,  has  so  far  remained  perfectly  intact. 
The  Bosnian  Roman  cement,  in  solution  of  sulphate  of  magnesium, 
showed  commencement  of  destruction  on  one  of  the  edges  after  18 
months;  the  sand  mortars  of  the  same  cement  are  still  intact. 
The  composition  of  these  two  Roman  cements  when  thoroughly 
baked  is  as  follows : 


Bavarian. 

Bosnian. 

Sand  and  clay 

Per  cent. 

6.381 
23.  881 
9.709 
4.052 
47.  229 
3.992 
4.237 

Not  det< 

Per  cent. 

2.920 
30.  180 
9.036 
3.669 
49.000 
2.215 
2.109 

3rmined. 

Silica 

Alumina           -         

Ferric  oxide 

Lime 

Magnesia  --   

Sulphuric  acid 

Manganese                                            ) 

Alkali  \ 

99.  481 

99.  129 

The  most  highly  calcareous  compounds  mentioned  in  the  begin- 
ning of  this  article  can  not,  as  has  been  shown  above,  form  in  these 
two  cements ;  if  the  formation  of  2  R2O3,  3  CaO  is  assumed,  then 
for  saturation  of  the  silica  there  remain  in  the  Bavarian  cements 
1.5  equivalents  of  lime,  that  is,  the  compound  2SiO2,  3  CaO,  and 
in  the  Bosnian  cement  1.35  equivalents  of  lime,  that,  is,  the  com- 
pound 3SiO.,,  4  CaO.  Hence  the  great  resistance  of  the  Roman 
cements  to  the  action  of  sea  water. 

Long  before  the  appearance  of  any  visible  symptoms  of  destruc- 
tion, the  existence  or  nonexistence  of  injury  will  become  manifest 
in  tests  of  strength,  especially  in  comparative  tests  of  test  pieces 
hardened  in  freshwater  and  others  hardened  in  sea  water,  and 
such  tests  evidently  form  the  correct  method  of  determining  the 
influence  of  sea  water. 


56 


INFLUENCE   OF    SEA    WATER   ON   HYDRAULIC    MORTARS. 


Test  pieces  having  a  great  surface  area  in  proportion  to  the  cross 
section,  to  be  tested  clearly,  are  best  adapted  for  such  tests.  Besides 
the  regular  tension  briquettes  I  have  employed  bars  30  centimeters 
long,  2  centimeters  high,  and  4  centimeters  broad.  These  bars  were 
tested  as  to  their  transverse  strength  by  centerloads  over  a  clear 
span  of  21.33  centimeters.  The  well  known  equation  for  the  coeffi- 


cient of  resistance,  C  —  - 


-        ,  ,  therefore,    renders   this  coefficient 

(per  square  centimeter)  equal  to  2  W,  that  is,  twice  the  breaking  load. 
As  mentioned  above,  it  is  not  advisable  to  employ  impervious 
mortars  for  testing  the  influence  of  sea  water  on  hydraulic  binding 
media,  because  the  time  required  for  obtaining  results  would  be 
unduly  increased,  and  because  it  is  evident  that  methods  of  test 
are  the  better  the  sooner  they  lead  to  results.  Therefore,  mortars 
of  1  :  5  are  much  preferable  to  mortars  of  1:3. 

In  accordance  with  this  line  of  reasoning  I  have  undertaken  the 
second  series  of  tests,  which  is  not  yet  completed.  The  Stettin 
Portland  cement  (A),  the  same  Portland  cement  worked  dry  con- 
taining 9  per  cent  alumina  (B),  the  lime  of  Theil  (C),  and  the 
Bavarian  Roman  cement  (D)  are  the  same  as  those  employed  for 
the  first  series  of  tests.  The  composition  of  these  cements  in  a 
baked  condition  is  as  follows  : 


A 

B 

c 

D 

Silica 

Per  cent. 
21.712 

Per  cent. 

21  331 

Per  cent. 

23  880 

Per  cent. 

23  881 

Alumina  

5.805 

8.918 

2.570 

9.709 

Ferric  oxide            

2.949 

2.695 

0.880 

4  052 

Lime  _.  

64.  851 

63.  776 

69  150 

44  263 

Magnesia 

1.030 

0  805 

1  600 

3  992 

Potash 

0.748 

0  777 

0  140 

Soda  -  . 

0.160 

0.101 

0.070 

Sulphate  of  lime  

2.468 

1.631 

1  090 

7  203 

Residuum  

0.357 

0.123 

6  381 

100.  080 

100.  157 

99.  380 

99.481 

Standard  tensile  briquettes  were  shaped  from  mortars  mixed  in 
the  proportion  of  1 :  5  with  Berlin  standard  sand. 

In  the  place  of  sea  water  the  artificial  sea  water  described  above 
was  employed.  Unless  otherwise  stated  the  test  pieces  were  first 
allowed  to  harden  in  moist  air  for  24  hours.  Those  under  S  were 
stored  on  edge  in  sea  water,  and  those  under  R  in  fresh  water ;  the 
additional  index  "e"  signifies  that  before  being  submerged  in  sea 
water  the  briquettes  were  kept  in  air  for  8  weeks  (being  moist- 
ened daily)  to  allow  the  absorption  of  carbonic  acid. 

The  test  pieces  made  of  lime  of  Theil  were  first  kept  in  moist 
air  for  28  days  and  then  8  weeks  in  air,  being  moistened  daily. 


INFLUENCE   OF  SEA  WATER  ON   HYDRAULIC   MORTARS. 


57 


Tlie  time  of  test  is  counted  from  the  day  previous  to  immersion  in 
water.  At  the  present  writing  the  test  pieces  have  been  under 
treatment  for  20  months. 

Each  of  the  following  figures  is  the  mean  of  ten  individual  tests, 
and  represents  kilograms  per  square  centimeter : 


Age  since 
immersion. 


A  i; 


A  S 


ASe 


BR 


BS       BSe 


CB 


CS 


CSe 


DB 


DS       DSe 


7  days 

28  days 

90  days 


7.23 
10.09 
11.60 


1  year _„   16 


7.54 
10.40 
16 


15.93 
15.25 
15.28 
6. 50  to  18 


10.50  7.86  j  17.05 
12.68  j  6.91  I  17.75 
15  i  9.10  j  15.89 
16.70  11.20  2  to  15 


3.81 
5.17 

8.38 
13.25 


4.96 
6.50 
10.86 
15.20 


7.75 
6.97 


12.50 


9.22 


2.86 

5.11 

9.68  I  11.43 

14.43  I  14.12 


6.27     13. 


12 
13.50 
14.66 
15.44 


Cement  A  was  then  mixed  with  trass,  the  following  being  taken 
into  consideration: 

100  parts  by  weight  of  trass  contain — 

10  to  12  parts  of  water  and  loss  in  baking; 

20  to  30  parts  of  hydraulic  silica  and  alumina ; 

60  to  65  parts  of  minerals  acting  as  sand. 

Of  the  trass  employed  41  per  cent  was  held  by  a  sieve  of  2,500 
meshes  per  square  centimeter ;  in  an  air-dried  condition  its  compo- 
sition was  as  follows : 

Percent. 

Hygroscopic  water 4. 141 

Water  of  crystallization 6. 899 

Lossat900°C 0.202 

Silica 53.583 

Alumina 19.  008 

Oxide  of  manganese* 0. 115 

Ferricoxide* 4.193 

Lime 1.736 

Magnesia 1. 652 

Potash 4.147 

Soda 4.242 

Titanic  acid \ 

Chlorine >•  Not  determined. 

Phosphoric  acid.  ) 

Sulphuric  acid 0. 107 

100. 025 
With  a  10  per  cent  lye  of  caustic  soda  this  trass  rendered: 

(a)  Digested  for  10  hours  in  a  water  bath —  per  cent. 

Hydraulic  silica 16.543 

Hydraulic  alumina 4.  810 

(6)  Digested  for  24  hours  in  a  water  bath — 

Hydraulic  silica 16.  708 

Hydraulic  alumina 6. 043 


*Iroii  and  manganese  were  counted  as  oxides,  although  there  also  existed 
protoxides  of  them. 


INFLUENCE    OF    SEA   WATER   ON   HYDRAULIC    MORTARS. 


The  following  two  mortars  were  made  : 


E. 


1  part  cement  A...  )  1  25  binding  medium  ,  that  is,  somewhat  richer 


1  part  trass ) 

4  parts  standard  sand 

1 

0.5 
(  4. 5  parts  standard  sand 


4.  60  sand 


than  1:4. 


25  binding  medium  *  that  is>  somewhat 

*•»»  sand  ----------  f     poorer  than  1  ;  4. 


In  the  following  table,  which  renders  the  results  of  tests  of 
strength  with  these  mortars,  the  letters  R  and  S  have  the  same 
meaning  as  above;  each  of  the  figures  is  the  mean  of  ten  indi- 
vidual tests: 


Age. 

E  K 

E  3 

F  R 

.  F  S 

7  days 

9.80 

11.80 

11.05 

10.10 

28  days 

19.15 

28.00 

16.90 

19.55 

90  days 

26.70 

35.70 

21.80 

23.65 

1  year 

30.95 

39.50 

27.55 

24.  59 

It  has  been  shown  that  out  of  100  parts  by  weight  of  Portland 
cement,  with  a  mean  percentage  of  lime,  there  will  separate  25 
parts  of  CaO  (33  parts  of  CaH2O2).  If  100  parts  of  trass  are 
added  (which,  for  example,  contain  16.5  parts  of  silica  and  5.14 
parts  of  alumina,  both  of  them  able  to  combine)  the  formation  of 
SiO2CaO  would  require  15.4  parts  of  CaO,  and  the  formation  of 
2  A12O3,  3  CaO  would  require  4.2  parts  of  CaO,  that  is,  a  total  of 
19.6  parts  of  CaO;  therefore  the  formation  of  a  silicate  richer  in 
lime  than  the  monosilicate  is  possible,  and  an  admixture  of  125 
parts  or  more  of  trass  per  100  parts  of  Portland  cement  is  very 
probably  advisable,  all  the  more  so  since  compounds,  even  of 
2  SiO2  to  1  or  2  of  CaO,  become  very  hard  and  are  doubtless  more 
stable  than  the  monosilicate.  At  any  rate  the  admixture  should 
be  the  greater  the  higher  the  percentage  of  lime  in  the  cement ; 
this  holds  good,  likewise,  for  hydraulic  limes. 

In  accordance  with  this  an  injurious  influence  of  sea  water  is 
perceptible  in  mortar  F  S  after  the  lapse  of  a  year ;  in  this  mixture 
of  100  parts  of  cement  and  50  of  trass,  only  10  parts  of  the  free  lime 
will  be  bound  with  sufficient  permanence,  while  15  parts  of  lime 
will  remain  free  to  enter  new  compounds,  and  even  were  the  sili- 
cate 2  SiO2  3  CaO  and  the  aluminate  2  AlaO8  5  CaO  to  form,  there 
still  would  remain  10  parts  by  weight  of  lime  free  to  be  acted 
upon  by  the  sulphates  of  the  sea  water. 

Later  experiments,  commenced  in  October,  1895,  refer  to  mortars 
composed  of  Portland  cement  and  lime  of  Theil,  with  admixtures 
of  trass  in  such  proportion  that  the  richness  of  the  mortar  is  rather 


INFLUENCE   OF   SEA   WATER   ON  HYDRAULIC   MORTARS. 


59 


diminished  than  increased  by  them.     These  mortars  are  composed 
as  follows : 

G.  Portland  cement  with  9  per  cent  alumina  (as  above:  B)  1  :  5 

Berlin  standard  sand. 

H.  Same  cement  1  part,  trass  1  part,  Berlin  standard  sand  6  parts. 
I.     Same  cement  1  part,  trass  1  part,  Berlin  standard  sand  6. 75  parts. 
K.   Lime  of  Theil  (as  above :  C)  1  :  5  Berlin  standard  sand. 
L.    Lime  of  Theil  1  part,  trass  1  part,  Berlin  standard  sand  5  parts. 
M.  Lime  of  Theil  1  part,  trass  1  part,  Berlin  standard  sand  6  parts. 

The  ratio  of  binding  medium  to  sand  is  as  follows : 

H.   1  part  by  weight  of  binding  medium  to  nearly  5. 3  parts  of  sand. 
I.     1  part  by  weight  of  binding  medium  to  nearly  6  parts  of  sand. 
L.    1  part  by  weight  of  binding  medium  to  nearly  5  parts  of  sand. 
M.  1  part  by  weight  of  binding  medium  to  nearly  5.6  parts  of  sand. 

K,  L,  and  M  were  first  allowed  to  harden  in  moist  air  for  7  days. 

The  tests  of  mortars  E  to  M  are  to  be  extended  over  a  period  of 
three  years.  The  broken  briquettes  of  one  year's  age  and  above 
will  be  put  partly  into  a  2  per  cent,  partly  into  a  3  per  cent,  solu- 
tion of  sulphate  of  magnesium,  being  thus  exposed  to  much  more 
energetic  action  than  that  of  the  strongest  sea  water. 

In  the  following  table  there  are  rendered  the  results  of  tests  of 
strength  so  far  attained ;  each  result  is  the  mean  of  10  individual 
tests,  and  is  expressed  in  kilograms  per  square  centimeter ;  the  des- 
ignations R  and  S  have  the  same  meaning  as  heretofore ;  opposite  A 
is  rendered  the  specific  gravity  of  mortars  immediately  preceding 
the  tests : 


Age  since  immersion. 

GR 

GS 

HR 

HS 

IR 

IS 

KS 

LS 

MS 

28  days 

8.80 

6.35 

10.40 

21  65 

10  10 

20  45 

2  97 

11  75 

10  30 

£ 

2.162 

2  195 

2.227 

90  days       

10.25 

7.55 

16.85 

24.55 

16.55 

24.60 

2.3d* 

21.57 

20.10 

^ 

2.137 

2.172 

2.26 

2.28 

2.274 

2.292 

2  252 

2  250 

2.259 

*  Besides  a  decrease  of  strength  there  was  also  perceptible  in  the  90-day  test  pieces  of  lime  of 
Theil  an  expansion  of  the  outer  shell  here  and  there. 

It  is  at  once  apparent  from  these  figures  that  in  all  mortars  con- 
taining lime  which  becomes  free  during  the  hardening  process,  sea 
water  exercises  an  influence  opposed  to  an  increase  of  strength. 

The  process  of  crystallization  and  the  process  of  hardening  strug- 
gle with  each  other  in  these  cases,  the  former  generally  being  vic- 
torious and  causing  complete  destruction  of  the  cohesion  obtained 
through  the  latter. 

On  one  of  the  test  pieces  B  S  symptoms  of  decay  were  visible 
after  90  days ;  it  was  cracked  and  decomposed  to  such  an  extent 
that  it  broke  in  putting  it  into  the  testing  machine ;  on  the  out- 
line of  the  fracture  a  deposit  of  hydrate  of  magnesia  to  a  depth 
of  some  millimeters  was  visible.  At  the  end  of  a  year  the  deposit 


60          INFLUENCE    OF   SEA    WATER   ON    HYDRAULIC    MORTARS. 

of  magnesia  was  found  in  all  test  pieces  but  one  to  have  advanced 
to  a  depth  of  5  millimeters ;  the  same  condition  was  found  to  exist 
in  B  Se. 

Strange  to  say,  the  destruction  of  the  test  pieces  that  had  been 
exposed  to  absorption  of  carbonic  acid  was  even  a  more  rapid  one,* 
the  carbonated  shell  being  lifted  and  rolled  up,  as  in  A  Se  as  com- 
pared with  A  S,  and  in  C  Se  as  compared  with  C  S,  all  at  an  age  of 
one  year ;  D  Se  is  an  exception ;  all  test  pieces  made  of  mortar  D 
were  entirely  sound,  and  did  not  show  any  deposit  of  magnesia  at 
the  contours  of  fracture. 

The  above  figures  speak  for  themselves ;  an  admixture  of  trass 
(or,  generally,  of  effective  pozzuolanas)  to  hydraulic  binding  media 
that  are  too  rich  in  lime  (Portland  cement  and  hydraulic  limes), 
may  increase  two  or  three  fold  the  strength  of  mortars  made  from 
them,  and  may  make  these  mortars  stable  in  sea  water.  The  causes 
of  increase  of  strength  are  evident;  best  pozzuolanas  contain  a 
quantity  of  effective  hydraulic  factors  equivalent  to  those  in  the 
best  Portland  cement,  \  and  as  Portland  cement  contains  a  sufficient 
excess  of  lime  to  satisfy  fully  the  pozzuolanas,  it  is  not  surprising 
that  from  a  combination  of  both  materials  mortars  of  increased 
strength  should  result. 

Clearly  admixtures  containing  much  silica  and  little  alumina  are 
preferable ;  hence  an  admixture  of  kaolin,  in  the  case  of  maritime 
structures,  is  not  advisable. 

Summiiig  up,  it  may  therefore  be  asserted  that  scientific  and 
practical  proof  has  been  rendered  of  the  nonsuitability  for  maritime 
structures  of  hydraulic  binding  media  containing  more  lime  than  is 
required  for  the  formation  of  stable  hydrosilicates  and  aluminates 
(these  compounds  are  stable  only  when  their  percentage  of  lime  is 
small,  and  the  smaller  it  is  the  greater  will  be  their  stability). 

Mortars  mixed  according  to  my  suggestion,  besides  being  much 
more  stable  and  stronger,  are  also  considerably  cheaper,  and  it  is 
therefore  to  the  public  interest  that  they  should  be  employed 
generally  for  maritime  structures,  and  the  use  of  excessively  cal- 
careous hydraulic  binding  media  without  such  proper  admixtures 
should  be  discontinued. 

*  An  explanation  of  this  fact  may  perhaps  be  found  in  the  increased  porosity 
of  the  mortar  through  absorption  of  carbonic  acid  and  the  greater  ease  of  access 
thus  afforded  to  the  saline  solution.  The  hydrosilicate  of  lime  certainly  is  in  a 
colloidal  condition.  When  decomposed  by  carbonic  acid  crystalline  carbonate 
of  lime  will  form  and  the  silica  will  separate ;  but  as  compared  with  a  colloidal 
condition  this  process  of  carbonation  must  render  a  mortar  of  much  inferior 
density. 

f  According  to  my  latest  experiments  genuine  trass  contains  nearly  50  per  cent 
of  silica  and  alumina  able  to  enter  new  compounds. 


INFLUENCE   OF    SEA   WATER   ON   HYDRAULIC    MORTARS.          61 

This  solution  of  the  problem  is,  indeed,  the  most  favorable  one 
that  can  be  conceived.  No  changes  are  introduced  beyond  the 
judicious  use  of  such  well-approved  binding  media  as  the  true 
pozzuolanas,  among  which  none  is  superior  to  genuine  trass,  that 
is,  finely-ground  hydraulic  tufa  stone,  without  any  extraneous 
matter  whatsoever.  But  in  view  of  the  strength  and  the  energy 
of  set  of  Portland  cement  (with  which  the  mixture  is  made),  it  is 
quite  admissible  to  employ  not  only  trass,  but  also  the  pozzuolanas 
endowed  with  less  vigor  of  set.  Theoretical  computation  as  well 
as  practical  tests,  which  can  be  made  rapidly,  will  in  each  case 
show  which  mixture  is  the  one  best  adapted  to  the  circum- 
stances. *  *  * 

It  is  not  my  business  to  investigate  how  consumers  will  look 
upon  this  matter,  but  I  still  adhere  to  the  view  that  the  manufac- 
turer is  not  only  the  best  judge  of  the  admixtures  required  by 
his  particular  product,  but  also  best  able  to  carry  out  the  particu- 
lar work  of  mixing.  *  *  *  But  this  point  should  be  decided 
by  the  consumers  themselves. 

This  discussion  would  doubtless  have  been  of  greater  value  if  its 
publication  had  been  postponed  for  some  years,  but  my  advanced 
age,  as  well  as  the  consideration  of  a  number  of  great  maritime 
structures  soon  to  be  commenced  in  various  countries,  has  induced 
me  to  communicate  my  results  now.  May  my  work  be  repeated, 
tested,  and  carried  on  to  completion  by  men  of  science  and  by 
practical  men. 

#  *  *  #  *  *  * 

My  present  suggestion  is  based  on  the  fact,  long  ago  asserted  by 
me,  that  hydraulic  limes  and  Portland  cements  overloaded  with 
lime  can  be  improved  by  giving  them  such  admixtures,  either 
during  the  process  of  manufacture  or  during  the  gauging  of  the 
mortar. 

The  following  pozzuolanas  are  suitable  for  this  purpose :  Hydrau- 
lic silica  per  se,  opal,  infusorial  earth,  the  pozzuolanas  proper, 
trass,  santorin  earth,  powdered  glass,  burnt  alum  slate,  kaolin, 
brick  powder,  etc. 

Of  all  such  admixtures,  so  far  known,  genuine  trass  is  the  most 
effective. 

I  have  made  the  following  propositions  to  the  permanent  com- 
mittee in  regard  to  testing  hydraulic  binding  media  as  to  their 
resistance  against  sea  water : 

The  test  of  resistance  against  sea  water  is  made  with  porous 
mortar  of  1:5,  briquettes  being  kept  in  artificial  or  in  natural 
sea  water,  which  is  renewed  daily  during  the  first  four  weeks  and 
after  that  weekly ;  the  water  must  be  stirred  daily ;  tests  may  be 
made  of  tensile  crushing  or  transverse  strength. 


62          INFLUENCE   OF   SEA   WATER   ON   HYDRAULIC   MORTARS. 

Artificial  sea  water  is  a  solution  of  the  following  ingredients  in 
1  liter  of  water : 

Grams. 

Kitchen  salt 30 

Chloride  of  magnesium 3 

Sulphate  of  magnesium 3 

Sulphate  of  calcium 1.25 

No  bicarbonates  are  added,  the  object  not  being  to  retard  the 
action  of  sea  water;  but  bars  of  gypsum  wrapped  in  linen  are 
immersed  in  the  artificial  sea  water  in  order  to  keep  its  percentage 
of  sulphuric  acid  constant. 

REASONS. — The  action  of  sea  water  on  hydraulic  binding  media 
is  principally  a  chemical  one,  resulting  from  the  action  upon  each 
other  of  the  soluble  sulphates  contained  in  sea  water,  and  the  free 
lime,  that  is,  the  lime  becoming  free  during  set ;  the  ferrate,  the 
aluminate,  and  the  silicate  of  lime. 

This  action  will  become  apparent  soonest  in  porous  mortar,  tests 
of  strength  giving  the  earliest  evidence  of  it.  Therefore  test 
pieces  are  recommended  having  a  large  superficial  area  as  com- 
pared with  the  area  of  fracture,  and  consisting  of  mortar  gauged 
in  the  proportion  of  1  :  5.  Tensile  and  transverse  tests  are  prefer- 
able to  crushing  tests. 

Comparative  tests  of  briquettes  hardened  in  sea  water,  and  others 
hardened  in  fresh  water,  will  very  soon  enable  the  experimenter 
to  form  an  opinion  as  to  the  influence  of  sea  water  in  any  particu- 
lar case.  A  2  per  cent  solution  of  sulphate  of  magnesium  will  lead 
to  results  in  still  less  time. 

The  idea  of  the  action  of  salts  of  magnesium  on  hydraulic 
mortars  should  be  abandoned,  magnesia  not  acting  in  an  injurious 
manner,  but  rather  in  a  useful  one,  through  closing  of  pores ;  it 
separates  in  the  form  of  a  soft,  spongy  hydrate,  which  does  not 
cause  any  strains,  and,  being  insoluble,  remains  at  the  place  of 
formation.  Sulphuric  acid  only  acts  destructively,  and  therefore 
all  soluble  sulphates  act  so  likewise  (although  with  different  in- 
tensity), whether  they  be  sulphate  of  soda  (Vicat),  or  sulphate  of 
calcium  (Michaelis),  or  sulphate  of  magnesium. 


REPLY  TO  DR.  MICHAELIS'S  ARTICLE.* 

BY  THE  BOARD  OF  DIRECTORS  OF  THE  UNION  OF  GERMAN  PORTLAND  CEMENT 

MANUFACTURERS. 


In  reply  to  the  foregoing  article  we  desire  first  to  give  the  fol- 
lowing historical  data : 

When  in  the  beginning  of  the  eighties  the  mixing  of  Portland 
cement  with  slag  and  other  inferior  material  threatened  to  become 
too  prevalent,  the  board  of  directors  of  the  German  Portland  Cement 
Manufacturers  felt  called  upon  energetically  to  oppose  such  pro- 
ceedings, because  it  was  contrary  to  usage  and  justice  to  designate  a 
mixture  of  Portland  cement  with  other  materials  simply  as  ' '  Port- 
land Cement,"  and  secondly,  because  the  admixtures  employed, 
especially  slag,  diminished  the  quality  of  the  product,  and  the  ever- 
increasing  extent  of  the  practice  was  thus  calculated  seriously  to 
injure  the  reputation  of  the  German  cement  industry. 

The  manufacturers  then  attempted  to  prove  that  an  admixture 
of  slag,  so  far  from  depreciating,  actually  improved  the  quality  of 
cement  by  increasing  its  strength.  In  support  of  that  assertion, 
Dr.  Michaelis's  theory  was  quoted,  according  to  which  pozzuolanas 
(that  is,  compounds  containing  silica  and  alumina  able  to  combine) 
can  combine  with  the  lime  becoming  free  during  set  of  Portland 
cement,  forming  with  it  a  new  cement-like  compound,  thus  increas- 
ing the  strength  through  better  cementation  of  the  particles.  It  is 
not  to  be  denied  that  the  idea  forming  the  basis  of  this  theory  is  a 
correct  one,  inasmuch  as  limited  percentages  of  certain  admixtures — 
for  instance,  ultramarine  and  powdered  hydrate  of  silica — will 
increase  the  strength  of  Portland  cement.  But  for  the  pozzuo- 
lanas in  the  market  the  same  can  not  be  said.  For  instance,  admix- 
tures of  trass  and  of  granulated  slag  will  not  cause  an  increase  of 
strength.  But  slag  was  quite  frequently  used  as  an  admixture,  and 

*The  controversy  between  Dr.  Michaelis  and  the  Union  of  German  Cement 
Manufacturers  was  not  limited  to  the  technical  question  itself,  but  led  to  a  dis- 
cussion of  motives,  which  assumed  a  somewhat  personal  character  and  had  no 
bearing  on  the  real  point  at  issue.  For  these  reasons  this  part  of  the  discussion 
has  been  omitted  from  the  above  translation,  the  omissions  in  each  case  being 
designated  in  the  customary  way. 

(63) 


64          INFLUENCE   OF   SEA   WATER   ON   HYDRAULIC   MORTARS. 


it  is  apparent  from  the  following  table  that  the  strength  of  cement 
was  thereby  diminished  : 

TABLE  No.  1. 

[1  cement,  3  standard  sand.     Tensile  strength  in  kilograms  per  square  centimeter,  after  28  days1  hardening 

in  fresh  water.] 


Composition  of  cement. 

Without       U|tra. 

s,t.  «—• 

Trass. 

Slag. 

Fine  sand. 

Carbonate 
of  lime. 

Hydrate 
of  lime. 

20.8           

90  per  cent  cement           _) 

23.6 

20.4 

18.4 

18.2 

18.2 

19.0 

10  per  cent  admixture  j 
80  per  cent  cement    [ 

24.5 

18.1 

15.4 

15.7 

16.1 

15.1 

20  per  cent  admixture  j 

_       _          20.  3 

15.7 

13.  5 

13.9 

13.6 

10.2 

33  per  cent  admixture  j 
50  per  cent  cement  ") 

17.1 

12.5 

10.2 

11.0 

10.4 

50  per  cent  admixture  j 

If  these  admixtures  really  had  turned  out  to  be  improvements 
the  mixed  cements  would  doubtless  have  prevailed.  Instead  of 
that,  the  practice  of  mixing  has  decreased  more  and  more.  *  *  * 
It  may  also  be  stated  here  that  up  to  the  present  day  no  practi- 
cally applicable  material  is  known,  which,  as  an  admixture  with 
Portland  cement,  will  increase  its  strength  in  air  or  in  water. 

Passing  now  to  a  review  of  Dr.  Michaelis's  paper  we  shall  first 
discuss  his  theory  of  the  set  of  Portland  cement.     Michaelis  says : 
It  may  be  assumed  that  during  hydraulic  set  the  following  compounds  are 
formed : 

2SiO2,   3CaO  +  xH2O; 
2FeaO8,  4CaO  +  yH2O; 
2A12O3,  5CaO  +  zH2O. 

By  means  of  these  formula  and  an  analysis  of  Portland  cement 
he  computes  that  a  considerable  portion  of  the  lime  contained  in 
Portland  cement  remains  free  after  set ;  he  asserts  that  this  free 
lime  separates  in  form  of  crystals  to  the  amount  of  about  25  per 
cent  in  an  average  Portland  cement,  and  that  it  exercises  an 
injurious  influence,  especially  in  sea  water,  where  through  chemi- 
cal changes  it  will  cause  destruction. 

But  Dr.  Michaelis  has  nowhere  furnished  proof  that  the  above 
three  compounds  of  lime  did  form  during  his  experiments,  or 
that  they  actually  do  form  during  the  process  of  hydraulic  set  of 
Portland  cement.  He  has  likewise  failed  to  prove  that  the  forma- 
tion of  compounds  with  a  higher  percentage  of  lime  than  the 
above-named  ones  is  impossible  during  the  hardening  of  Portland 
cement.  Consequently  his  assertion  that  25  per  cent  of  lime  sepa- 
rates during  set  of  Portland  cement  is  not  established.  But  even 


INFLUENCE   OF    SEA   WATER   OX    HYDRAULIC    MORTARS.          65 

supposing  it  were,  this  would  not  justify  the  conclusion  that  this 
25  per  cent  of  lime  is  injurious.  As  a  matter  of  experience,  Port- 
land cement,  if  suitably  employed,  is  the  very  one  of  all  binding 
media  which  has  given  more  satisfaction  than  any  other  in  air, 
fresh  water,  and  sea  water.  The  high  percentage  of  lime  con- 
tained in  Portland  cement  is  one  of  its  characteristic  features ;  it 
enables  us  to  burn  this  cement  up  to  vitrification,  and  thus  endow 
it  with  great  density  and  those  other  excellent  qualities  which  dis- 
tinguish Portland  cement  so  favorably  from  all  other  binding 
media. 

We  can  not  here  enter  upon  all  the  assertions  made  by  Dr. 
Michaelis,  but  must  restrict  ourselves  to  a  discussion  of  his  prin- 
cipal theme,  that  is,  the  behavior  of  Portland  cement  in  sea  water, 
and  his  suggestions  for  the  improvement  of  sea- water  mortars. 

During  the  hardening  of  Portland  cement  in  sea  water  the 
hydrate  of  lime  being  then  formed  is  acted  upon  principally  by 
chloride  of  magnesium  and  sulphate  of  magnesium  (besides  smaller 
amounts  of  other  sulphates).  The  chloride  of  magnesium  changes 
into  chloride  of  calcium  and  hydrate  of  magnesia ;  the  former  is 
dissolved,  while  the  latter,  being  insoluble,  remains  in  the  mortar. 
A  portion  of  the  hydrate  of  lime,  which  under  ordinary  circum- 
stances serves  for  better  cementation  of  the  mortar,  thus  increas- 
ing its  strength,  is  therefore  lost  in  sea  water. 

The  sulphate  of  magnesia  combines  with  the  hydrate  of  lime 
contained  in  Portland  cement,  forming  sulphate  of  calcium  and 
hydrate  of  magnesia.  If  the  sulphate  of  calcium  as  such,  and 
more  especially  a  double  compound  of  it,  viz,  sulphate  of  alumina 
and  lime,  could  form  in  sufficient  quantities,  they  would  indeed 
endanger  the  cement  mortar,  as  both  of  these  compounds,  and 
especially  the  last-named  soluble  compound,  in  expanding  consid- 
erably, absorb  a  great  deal  of  water,  and  may  thus  destroy 
cohesion.  Continued  action  of  the  sulphates  contained  in  sea 
water  is,  however,  soon  energetically  opposed  by  the  increase  of 
closeness  of  grain  taking  place  during  hardening.  In  this  way, 
and  by  magnesia  separating  in  the  pores,  the  infiltration  of  sea 
water  is  gradually  checked  and  its  action  stopped.  The  correct- 
ness of  this  view  has  been  shown  by  R.  Dyckerhoff's  experiments, 
according  to  which,  absorption  of  sulphuric  acid  by  Portland 
cement  mortar  hardening  in  sea  water  diminishes  as  time  passes, 
rich  cement  mortars  absorbing  less  and  therefore  suffering  less 
than  poor  mortars. 

The  above-described  chemical  processes  furnish  an  explanation 
of  the  fact  that  the  strength  of  Portland  cement  mortar  is  less  in 
sea  water  than  in  fresh  water. 

15671 5 


06          INFLUENCE   OF   SEA   WATER   ON   HYDRAULIC   MORTARS. 

But  from  Dr.  Michaelis's  paper  it  would  appear  that  Portland 
cement  will  not  last  at  all  in  sea  water. 

The  best  criterion  of  a  building  material  is  the  experience  gained 
during  its  practical  use  on  a  large  scale. 

Turning  to  practice,  therefore,  we  find  numerous  maritime  con- 
structions on  the  shores  of  the  German  Ocean  and  of  the  Baltic 
furnishing  proof  of  the  durability  of  Portland  cements  during  long 
periods.  The  seacoast  forts  of  Copenhagen,  for  instance,  which 
were  built  nearly  forty  years  ago,  are  to  this  day  in  a  state  of  per- 
fect preservation.  We  intentionally  name  these  forts,  as  they  were 
built  with  Stettin  cement  of  the  same  chemical  composition  as 
cement  A,  which  was  used  by  Dr.  Michaelis  in  the  experiments 
leading  him  to  the  conclusion  that  Portland  cement  will  not  last  in 
sea  water. 

We  also  wish  to  point  to  a  publication  made  in  1889  by  a  com- 
mission on  limes,  cements,  and  mortars,  which  was  appointed  by 
the  French  ministry  of  public  works.  This  commission  has  made 
experiments  extending  over  a  period  of  ten  years,  on  hydraulic 
limes,  on  Roman  and  Portland  cements,  on  blocks  of  concrete  as 
well  as  of  masonry  immersed  in  sea  water,  and  has  found  that  none 
of  the  hydraulic  limes  under  test  resisted  the  action  of  sea  water 
longer  than  from  four  to  five  years.  Even  lime  of  Theil  did  not 
resist  much  longer,  at  least  not  when  exposed  to  agitated  sea  water, 
although  great  power  of  resistance  against  sea  water  is  frequently 
claimed  for  that  lime.  Blocks  formed  of  Roman  cement  were  like- 
wise found  to  have  been  injuriously  affected  after  from  eight  to 
ten  years,  while  the  Portland  cement  blocks  were  the  only  ones 
that  remained  intact  after  a  lapse  of  ten  years. 

On  the  other  hand,  it  can  not  be  denied  that  there  have  been  fail- 
ures of  Portland  cement  in  maritime  structures.  It  is,  however,  sus- 
ceptible of  proof  that  in  all  such  cases  there  have  been  either  errors 
of  construction,  or  the  mortar  employed  has  been  too  poor  and  there- 
fore too  porous.  For  failures  arising  from  conditions  of  this  kind, 
Portland  cement,  as  such,  can  not  be  held  responsible.  *  *  * 

Tests  now  in  progress  at  Sylt,  under  the  auspices  of  the  Royal 
Department  of  Public  Buildings,  have  so  far  resulted  in  all  bri- 
quettes of  Portland  cement  exposed  to  sea  water  having  remained 
intact  and  continued  to  increase  in  strength,  although  not  as  much 
as  in  fresh  water,  while  mortars  of  Portland  cement  and  lime,  and 
especially  mortars  of  trass  and  lime,  have  been  injuriously  affected 
by  sea  water. 

Dr.  Michaelis  recommends  adding  trass  to  Portland  cement  in 
order  to  increase  its  power  of  resistance  against  the  chemical  action 
of  sea  water,  his  theory  being  that  the  lime  becoming  free  during 


INFLUENCE   OF   SEA    WATER   ON  HYDRAULIC   MORTARS.          67 

set  will  combine  with  the  silica  and  alumina  of  the  admixture, 
forming  a  chemically  stable  compound. 

In  a  series  of  tests  executed  by  him  he  has  obtained  through  an 
admixture  of  trass  a  considerable  increase  of  strength,  especially 
when  hardening  took  place  in  sea  water. 

We  desire  here  to  call  the  reader's  attention  to  the  difference 
between  the  practice  of  giving  Portland  cement  an  admixture,  and 
the  practice  of  mixing  into  the  mortar  some  additional  material 
besides  Portland  cement  and  sand.  If  a  part  of  the  cement  is 
replaced  by  other  material  (excepting  ultramarine  and  similar 
compounds),  then  according  to  Table  No.  1  the  mortar's  strength 
is  diminished. 

But  if  limited  quantities  of  finely-ground  material,  such  as 
hydrate  of  lime,  powdered  sand,  etc. ,  are  added  to  a  poor  cement 
mortar,  then  a  filling  of  pores  takes  place,  which  will  cause  an 
increase  of  strength.  Evidently  this  is  not  an  improvement  of 
cement,  but  of  mortar.  In  the  case  of  water  storage  especially, 
trass  acts  better  than  other  materials,  because,  aside  from  the  fill- 
ing of  pores,  a  further  increase  of  density  takes  place  through  the 
trass  combining  with  hydrate  of  lime  separating  from  the 
cement. 

In  rich  mortars,  however,  that  are  less  porous,  no  improvement 
will  be  effected  by  the  same  admixtures.  Even  trass,  notwith- 
standing its  free  silica,  will  not  improve  them,  the  greater  volume 
of  water  absorbed  by  it  causing  inferior  density,  without  any  addi- 
tional strength  of  cohesion  between  the  particles. 

For  the  purpose  of  testing  the  action  of  pozzuolanas  during  set 
of  cement  mortar  in  sea  water,  we  have  commenced,  like  Dr. 
Michaelis,  several  series  of  tests  with  cement  mortars  having  an 
admixture  of  trass. 

For  these  tests  we  have  selected  principally  rich  mortars,  because 
these  are  mostly  used  for  maritime  structures.  But  for  the  pur- 
pose of  comparison  there  was  also  tested  one  poor  mortar  (1:4). 
The  storage  water  used  was  sea  water  from  the  German  Ocean. 

The  cement  employed,  when  tested  according  to  standard  method 
(1 :  3,  28  days),  was  found  to  possess  a  tensile  strength  of  22.4  kilo- 
grams and  a  crushing  strength  of  238.8  kilograms  per  square 
centimeter.  The  trass  used  was  from  Plaidt ;  the  sand  was  quartz 
sand,  passing  through  a  sieve  of  60  meshes  per  square  centimeter 
and  held  by  one  of  900  meshes  per  square  centimeter.  All  mortars 
were  of  equal  consistency. 


68          INFLUENCE   OF   SEA   WATER   ON   HYDRAULIC   MORTARS. 

In  the  following  table  are  rendered  the  results  obtained  thus  far 


TABLE  No.  2. 

TENSILE  STRENGTH  AFTER  28  DAYS. 


1 

2 

3 

4 

5 

6 

7 

8 

Kind  of  storage. 

1  cement, 
1  sand. 

1  cement, 
1  trass. 

1  cement, 
1  trass, 
1  sand. 

1  cement, 
2  sand. 

1  cement, 
1  trass, 
2  sand. 

1  cement, 
4  sand. 

1  cement, 
1  trass, 
4  sand. 

ly  cement, 
4  sand. 

Fresh  water 

29.9 

29.3 

28.5 

23.5 

19.3 

11.5 

15.8 

16.2 

Sea  water 

29.3 

28.1 

,77 

22.4 

21.  G 

10.6 

15.2 

14.8 

CRUSHING  STRENGTH  AFTER  28  DAYS. 


Fresh  water  __ 

J  »i 

8 

287.8 

287.8 

258.0 

215.  5 

'     137.3 

124.8 

172.8 

From  this  table  we  perceive  that  rich  mortars  with  only  1  or  2 
parts  of  sand  do  not  experience  any  increase  of  strength  through 
an  admixture  of  trass,  even  when  hardened  in  sea  water  (columns 
1-5).  Even  the  mortar  1  cement  to  1  trass  is  not  any  stronger 
than  the  mortar  1  cement  to  1  sand. 

The  poor  mortar,  1  cement  to  4  sand,  however,  is  improved  by  an 
admixture  of  trass  (columns  6,  7). 

The  tensile  strength  of  mortar  of  1  cement,  1  trass,  and  4  sand, 
after  28  days,  according  to  our  tests,  is  not  any  higher  in  sea  water 
than  in  fresh  water,  while  Michaelis  finds  it  to  be  9  kilograms 
stronger  in  sea  water  than  in  fresh  water. 

There  is,  therefore,  an  important  contradiction  in  the  two  results. 

A  second  brand  of  cement  has  rendered  the  same  results  for  the 
mortar  of  1  cement  and  4  sand,  with  and  without  trass.  But  in  the 
case  of  this  cement  the  mortar  of  1  cement  and  2  sand  was  improved 
by  an  admixture  of  trass  when  stored  in  sea  water. 

It  is  worthy  of  notice  that  in  the  above  table  the  mortars  mixed 
with  trass  have  a  comparatively  smaller  crushing  strength,  and, 
again,  that  an  addition  of  |  cement  to  the  mortar  1 :  4  has  at  least 
the  same  effect  as  one  of  trass.  *  *  * 

Our  preliminary  investigations  on  the  employment  of  trass  as  an 
admixture  for  cement  mortar  in  the  case  of  maritime  structures 
have  rendered  results  essentially  different  from  those  of  Dr. 
Michaelis. 

Still  we  have  not  arrived  at  a  final  opinion  in  this  matter.  Tests 
continued  over  a  long  period  in  the  ocean  itself  will  be  required 
to  decide  whether  admixtures  of  trass  are  advantageous  in  cement 
mortars  for  maritime  purposes. 


THE  INFLUENCE  OF  SEA  WATER  ON  MORTARS.* 
BY  E.  CANDLOT. 


Since  Vicat's  important  investigations  many  theories  have  been 
advanced  concerning  the  decomposition  of  mortar  by  sea  water. 
Although  these  theories  may  furnish  valuable  hints  as  to  the  selec- 
tion and  treatment  of  mortar  materials,  the  results  of  practice  alone 
form  a  safe  guide  for  the  constructing  engineer. 

But  practical  tests  are  of  value  only  when  they  extend  over  a 
sufficient  length  of  time.  A  period  of  fifteen  or  twenty  years  is 
frequently  required  to  judge  of  a  certain  material  employed  under 
certain  conditions. 

If  such  practical  observations  are  made  systematically  and  care- 
fully their  value  is  very  great. 

Investigations  in  the  harbor  of  La  Rochelle  since  1856  are  of 
great  importance  in  this  direction,  since  they  extend  over  a  period 
of  forty  years  and  have  been  made  under  conditions  adapted  closely 
to  practice.  We  [Candlot]  are  indebted  to  Messrs.  Thurninger  and 
Viennot,  the  former  chief  and  the  latter  ingenieur  des  ponts  et 
chausse'es,  for  a  summary  of  the  observations  made  so  far,  and  we 
believe  that  the  conclusions  drawn  from  them  will  be  read  with 
great  interest  by  all  concerned  in  the  question  of  the  influence  of 
sea  water  on  mortars. 

Mr.  Viennot  intends  later  on  to  publish  a  complete  report  ren- 
dering all  details  and  all  results  found  during  this  long  series  of 
investigations. 

A  first  series  of  cubical  blocks  of  60  centimeters  length  of  edge 
was  exposed  to  the  open  sea  during  the  period  from  1856  to  1875; 
these  blocks  were  above  the  water's  surface  at  each  low  water.  The 
mortars  were  composed  of  hydraulic  limes  of  different  origin,  of 
natural  cements  from  Ponilly,  Vassy,  etc.,  of  artificial  pozzuolanas 
mixed  with  various  kinds  of  lime  and  sand,  of  admixtures  of  lime 
and  cement,  and  finally  of  trass  from  Andernach,  mixed  with  var- 
ious kinds  of  lime  and  sand. 

Nearly  all  blocks  had  completely  lost  their  cohesion  after  periods 
of  various  length.  The  rest  were  strongly  affected  or  nearly 
destroyed.  Only  a  few  blocks  of  Portland  cement  were  experi- 
mented upon,  of  which  the  blocks  of  mortar  of  English  cement 
(1857),  of  Portland  cement  from  Dauphine's  (1859),  and  of  Portland 

*  From  TJionindustrie-Zeitung,  February,  1897. 


70          INFLUENCE    OF    SEA   WATER   ON   HYDRAULIC    MORTARS. 

cement  from  Boulonnais  (1875)  were  in  very  good  condition.    Blocks 
of  neat  cement  (English  and  French)  were  decomposed. 
From  these  tests  Viemiot  draws  the  following  conclusions : 

(1)  Neat  cements  are  destroyed  more  rapidly  than  mortars  of  a 
certain  composition. 

(2)  Mortars  made  of  1  volume  of  cement  to  1  volume  of  sand, 
and  again  of  1  volume  ol  cement  to  2  of  sand  (that  is,  about  1,300 
kilograms  and  650  kilograms  respectively  of  cement  to  1  cubic 
meter  of  sand)  are  those  which  offer  the  greatest  resistance  to  sea 
water.     They  will  last  for  20,  3G,  and  38  years. 

In  1880  Thurninger  commenced  a  new  series  of  tests  with  blocks 
of  masonry  and  of  concrete  made  of  lime  of  Theil  mortar.  The 
length  of  edge  of  the  cubical  blocks  was  40  centimeters. 

On  July  1,  1895,  the  masonry  blocks  had  disappeared,  their 
destruction  having  commenced  four  years  after  their  exposure. 
Out  of  thirty-two  concrete  blocks  only  twenty-six  remained,  but 
they  were  in  a  state  of  advancing  decomposition  and  certain  sooner 
or  later  to  crumble  away  entirely. 

A  second  series  of  tests  with  cubical  blocks  of  40  centimeters 
length  of  edge  was  also  commenced  in  1880.  These  blocks  were 
submerged  in  sea-connected  basins,  the  water  in  which,  on  the  aver- 
age, was  renewed  twice  during  each  day ;  as  a  rule  the  blocks  do 
not  show  above  the  water's  surface.  Their  number  at  present  is 
193,  and  they  consist  chiefly  of  various  limes,  French  and  foreign 
cements.  Out  of  nine  blocks  of  natural  cement  from  Lot  et- Garonne-, 
two  have  crumbled  away.  Three  blocks  of  cement  from  Grdnotte 
were  made  in  1881,  eight  in  1882,  and  six  in  1887;  of  these  blocks 
five  have  been  destroyed. 

Experimenting  with  slag  cements  was  not  commenced  until  1891 ; 
out  of  twenty  blocks  submerged  between  1891  and  1893,  fourteen 
at  present  are  crumbling  away;  four  others,  submerged  in  1894 
and  1895,  are  still  in  good  condition. 

Out  of  thirty-one  masonry  blocks  laid  in  Portland  cement  mortar 
and  submerged  between  1881  and  1892,  twenty-two  are  still  intact, 
while  nine  have  commenced  to  disintegrate.  Among  the  older 
blocks  there  are  three  laid  in  English  cement  mortar  (1883)  and 
three  laid  in  Boulonnais  cement  mortar  (1895)  of  great  power  of 
resistance. 

According  to  Viennot,  these  tests  point  to  the  following  con- 
clusions : 

(1)  Mortars  of  hydraulic  lime,  mixed  in  any  proportion,  in  most 
cases  commence  to  disintegrate  after  one  or  two  years'  immersion 
in  sea  water;    they  crumble  into  pulp  after  periods  varying  in 
length,  but  apparently  not  exceeding  fifteen  years. 

(2)  Concrete  resists  better  than  masonry,  owing  to  the  greater 
density  imparted  to  it  by  ramming. 


INFLUENCE   OF   SEA    WATER    OX    HYDRAULIC    MORTARS.          71 

(3)  Rapid-setting  cements  may  commence  to  disintegrate  after 
six  or  eight  years,  but  again  it  has  been  observed  that  they  may 
last  longer  than  thirty-eight  years  without  crumbling. 

(4)  The  mortars  offering  the  greatest  resistance  are  those  con- 
sisting of  1  part  cement  to  1  or  2  parts  respectively  of  sand  (1,300 
kilograms  or  650  kilograms  respectively  of  cement  per  cubic  meter 
of  sand). 

This  mixture  corresponds  to  the  weight  of  cement  required  to 
fill  the  spaces  between  the  grains  of  sand.  These,  therefore,  are 
the  least  porous  mortars. 

A  theory  of  the  resistance  of  mortars  to  sea  water  can  only  be 
of  speculative  interest,  unless  it  is  based  on  practical  investiga- 
tions of  long  duration.  The  experiments  made  at  La  Rochelle, 
during  nearly  forty  years,  form  a  safe  basis  of  discussion  of  this 
matter,  and  we  may  now  proceed  to  investigate  the  question  why 
Portland  cement  appears  to  be  superior  in  maritime  structures  to 
any  other  hydraulic  binding  medium,  and,  again,  what  conditions 
must  be  filled  by  mortars  in  order  to  make  them  proof  against  the 
destructive  influence  of  sea  water.  The  principal  fact  clearly  and 
unmistakably  proved  by  the  La  Rochelle  tests  is  this :  That  none  of 
the  hydraulic  binding  media  so  far  known  will  resist  the  action 
of  sea  water  if  the  latter  is  able  to  penetrate  into  the  mortar. 
This  conclusion  is  to  be  regretted,  because  it  excludes  the  hope 
that  the  question  of  the  behavior  of  mortars  in  sea  water  may  be 
solved  within  a  reasonable  time  by  purely  chemical  investigations. 

Verification  through  time  tests  is  always  indispensable,  as  theory 
is  too  often  contradicted  by  facts.  But  these  tests  have  settled  one 
very  important  point  in  an  unquestionable  way,  viz,  the  necessity 
of  employing  only  such  hydraulic  binding  media  as  do  not  contain 
any  free  lime,  which  may  slake  after  gauging. 

Destruction  of  mortars  exposed  to  the  action  of  sea  water  may 
occur  in  a  twofold  manner ;  either  it  proceeds  from  the  exterior  to 
the  interior,  which  is  commonly  the  case,  or  it  commences  in  the 
interior,  in  which  case  it  is  caused  by  the  hydrating  of  free  lime 
or  free  magnesia. 

When  the  silica  and  alumina  contained  in  homogeneous  cement 
is  not  sufficient  to  saturate  the  lime*  contained  in  it,  then  there 
will  be  free  lime.  The  total  quantity  of  lime  must  never  exceed 
the  following  proportion : 

SioT-SiA<3(H'leChatelier)- 

Free  lime  is  also  found  in  cements  of  normal  composition,  but 
of  imperfect  mixture.  This  will  occur  in  natural  cements  which 


*  Magnesia  is  always  present  in  small  quantities ;  the  lime  only  is  of  importance. 


72          INFLUENCE    OF    SEA   WATER   ON   HYDRAULIC   MORTARS. 

are  mixtures  of  separately-burnt  stones,  some  containing  an  excess 
of  lime,  others  an  excess  of  alumina. 

In  hydraulic  limes  free  lime  is  due  to  imperfect  slaking.  The 
excess  of  lime  is  not  injurious  after  it  has  been  slaked.  The 
magnesia,  separated  from  the  sulphate  of  magnesia  by  the  lime 
contained  in  the  mortar,  is  also  harmless. 

Free  lime  is  most  dangerous  when  contained  in  compounds  burnt 
at  a  high  temperature.  In  these  cases  it  absorbs  water  very  slowly, 
and  a  considerable  time  may  pass  after  gauging  the  mortar  before 
it  acts.  If  there  is  so  much  of  it  that  its  expansive  force  is  greater 
than  the  cohesion  of  the  mortar,  then  the  latter  is  either  torn 
asunder  or  cracks  are  caused  through  which  water  can  penetrate 
and  complete  the  work  of  destruction.  If  such  mortar  hardens  in 
air,  or  in  fresh  water,  the  absorption  of  water  may  proceed  so 
slowly  as  to  allow  the  gradually-increasing  force  of  cohesion 
effectually  to  resist  expansion,  provided  the  percentage  of  lime  is 
not  too  great.  In  sea  water,  however,  the  absorption  of  water 
proceeds  with  greater  rapidity  and  the  mortar  is  not  allowed  to 
attain  a  sufficient  degree  of  strength.  The  expansion  caused  by 
free  lime  in  these  cases  is  of  a  very  destructive  nature. 

Therefore  only  binding  media  containing  no  free  lime  should 
be  employed  in  sea  water.  In  carefully-prepared  artificial  Port- 
land cements  it  is  easy  to  secure  this  condition.  The  natural  Port- 
land cements  that  have  been  calcined  at  a  high  temperature  are 
very  dangerous,  and  their  use  should  be  prohibited.  Incidents  of 
an  exceedingly  significant  nature,  that  have  occurred  during  prac- 
tical use  of  these  cements,  can  only  be  explained  by  expansion 
caused  by  free  lime.  Storage  in  pits  for  months,  and  even  years, 
is  not  sufficient  to  secure  in  every  case  hydrating  of  the  free 
lime. 

This  has  led  to  ignoring  the  water's  chemical  action  on  mortars 
and  to  study  their  behavior  from  a  physical  point  of  view  only. 
As  all  mortars,  without  any  exception,  are  decomposed  when  per- 
meated by  sea  water,  the  investigation  has  been  restricted  to  finding 
the  densest  mortars,  which  are  the  most  impervious  ones.  Labo- 
ratory experiments,  therefore,  should  be  abandoned,  as  they  can  not 
furnish  any  new  information ;  accommodation  to  the  conditions  of 
actual  use  is  required  to  consider  simultaneously  wave  action, 
difference  of  temperature,  etc. 

Laboratory  tests  have  only  rendered  one  piece  of  information, 
which,  while  being  of  great  importance,  could  readily  have  been 
foreseen ;  we  refer  to  the  great  influence  of  the  quality  of  sand. 
The  advantages  of  coarse  sand  are  universally  acknowledged  to-day 
and  the  use  of  fine  sand  has  been  discarded  everywhere. 


INFLUENCE   OF    SEA   WATER   ON   HYDRAULIC   MORTARS.          73 

When  the  density  of  mortars  is  studied  it  will  be  found  that  in 
this  quality  Portland  cement,  is  very  much  superior  to  all  other 
hydraulic  binding  media. 

We  believe  the  good  behavior  of  the  cement  mortar  gauged 
in  the  proportions  of  650  and  1,300  kilograms,  as  has  been  done 
at  La  Rochelle,  and  for  most  maritime  structures  during  the  last 
fifty  years,  is  principally  due  to  the  density  of  Portland  cement 
mortar.  This  binding  medium  possesses  the  greatest  specific 
gravity,  it  requires  the  smallest  quantity  of  gauging  water,  and, 
at  the  same  time,  will  bind  chemically  a  greater  quantity  of 
water  than  any  other  cement. 

Dr.  Michaelis  has  recently  published  an  exceedingly  interesting 
paper  on  decomposition  of  mortars  in  sea  water.  On  the  basis  of 
the  theory  that  the  best  resisting  cements  are  those  in  which  lime 
is  found  in  the  most  stable  compounds,  he  shows  that  Roman 
cements  contain  the  smallest  percentage  of  lime,  which  is  able  to 
act  on  the  sulphate  of  magnesium  present  in  sea  water  in  forming 
injurious  salts  (sulphate  and  sulphoaluminate  of  lime).  In  Port- 
land cement,  during  hardening,  there  separates  a  certain  quantity 
of  hydrate  of  lime,  which  strives  to  change  into  sulphate  or 
sulphoaluminate  of  lime. 

It  is  asserted  by  Dr.  Michaelis  that  even  lime  of  Theil  resists 
the  action  of  sea  water  better  than  Portland  cement.  We  are  far 
from  indorsing  this  theoretical  speculation,  which  is  completely 
contradicted  by  facts ;  the  latter  demonstrate  that  Portland  cement 
resists  the  action  of  sea  water  much  better  than  all  other  hydraulic 
binding  media,  notwithstanding  the  possible  inferiority  of  its 
chemical  composition. 

The  importance  attaching  to  the  density  of  mortars  has,  how- 
ever not  escaped  Dr.  Michaelis.  He  says : 

But  as  Roman  cements  are  burnt  at  red  heat,  or  at  moderate  red  heat  only, 
during  which  operation  they  do  not  condense,  they  must  be  pronounced  from  a 
physical  point  of  view  to  be  of  a  porous  nature ;  the  compounds  forming  during 
absorption  of  water  will,  therefore,  be  contained  in  them  in  a  much  swollen 
state ;  hence  the  mortars  produced  with  them  will  shrink  considerably  during 
air-drying,  through  loss  of  loosely-bound  water,  nearly  all  water  contained  in 
these  hydrates,  over  and  above  the  quantity  corresponding  to  the  hydrate  of 
lime  being  such  loosely -bound  water. 

Physically  the  hydraulic  limes,  the  best  representative  of  which  is  lime  of 
Theil,  are  quite  close  to  the  Roman  cements.  Their  density,  at  least  that  of 
the  so-called  light  ones,  is  generally  less  than  that  of  Roman  cements. 

From  a  physical  point  of  view  Portland  cement  is  much  superior  to  hydraulic 
limes,  because  it  acquires  great  density  through  vitrification  at  white  heat. 
During  set  the  pores  are  filled  more  completely  because,  the  particles  being  closer 
together,  there  is  in  the  same  space  much  more  swelling  substance.  The  mean 
proportion  of  mass  in  equal  spaces  is  for  Portland  and  Roman  cement  about  5 :  3, 
and  for  Portland  cement  and  hydraulic  limes  from  5: 2.5  to  5:  2;  vitrified  Port- 
land cement,  therefore,  has  a  much  greater  volume  weight,  and  consequently  its 


74          INFLUENCE    OF    SEA   WATER    ON    HYDRAULIC    MORTARS. 

mortar  attains  a  much  higher  degree  of  density,  or  rather  of  condensation,  since 
Roman  cements  and  hydraulic  limes  may  likewise  present  a  perfectly  close  grain. 

And  again  Dr.  Michaelis  adds : 

It  is  evident  that  closeness  of  grain— in  other  words,  imperviousness — is  a  very 
important  consideration. 

Even  if  the  quantity  of  binding  medium  employed  completely 
fills  all  voids  in  the  sand,  there  will  never  result  a  mortar  of  perfect 
density.  There  is  always  a  certain  quantity  of  voids.  In  gauging, 
air  bubbles  remain  inclosed  in  the  mass  and  are  not  removed  even 
when  the  greatest  care  is  exercised.  The  volume  of  voids  in  bind- 
ing media  is  about  the  same  in  all  of  them.  The  considerable  dif- 
ferences in  the  porosity  of  mortars  are  caused  by  voids  resulting 
from  the  excess  of  gauging  water.  In  the  first  place  the  various 
binding  media  require  very  different  percentages  of  water  for  gau- 
ging, and  in  the  second  place  the  volume  permanently  absorbed  as 
water  of  crystallization  differs  very  much. 

To  obtain  a  paste  of  standard  consistency,  there  are  required  for 
Portland  cement  25  per  cent  of  water  and  for  limes  and  Roman 
cements  from  40  to  60  per  cent  of  water.  Under  ordinary  circum- 
stances there  are  absorbed  as  water  of  crystallization  by  Portland 
cements  from  18  to  20  per  cent,  by  Roman  cements  and  hydraulic 
limes  from  8  to  10  per  cent,  and  by  slag  cements  from  5  to  6  per 
cent.  We  perceive  from  this  that  the  voids  caused  by  excess  of 
gauging  water  in  Portland  cement  amount  to  little  or  nothing, 
while  in  other  hydraulic  binding  media  they  will  run  up  as  high 
as  from  30  to  40  per  cent.  In  mortars,  the  sand  which  is  added  to 
the  cement  will  reduce  the  advantage  of  Portland  cement  in  this 
respect.  For  fine-grained  sand  a  great  deal  of  gauging  water  is  re- 
quired, whatever  may  be  the  nature  of  the  binding  medium.  When 
the  sand  is  coarse  and  the  percentage  of  cement  high,  then  the 
amount  of  water  required  for  gauging  is  not  much  more  than  that 
required  for  neat  cement.* 

It  has  been  shown  by  Alexandre  that  in  lime  mortars  the  volume 
of  voids,  that  is  to  say,  the  difference  between  the  apparent  and 
the  actual  volume  of  mortars  after  set,  varies  between  23  and  31 
per  cent;  in  cement  mortars  it  varies  between  13  and  31  per  cent, 
the  former  figure  corresponding  to  a  mixture  of  550  kilograms  of 
cement  with  1  cubic  meter  of  coarse  sand,  and  the  latter  figure 
corresponding  to  a  mixture  of  250  kilograms  of  cement  with  1  cubic 
meter  of  fine  sand. 

Mortar  made  of  650  kilograms  of  cement  and  one  cubic  meter  of 
coarse  sand  was  found  to  contain  only  9  per  cent  of  voids ;  for  lime 

*  Very  explicit  notes  on  this  subject  will  be  found  in  the  writings  of  Alexandre 
(Annales  des  ponts  et  chaussees,  September,  1890)  and  Feret  (Annales  des 
ponts  et  chaussees,  Juillet,  1892). 


INFLUENCE   OF   SEA   WATER   ON    HYDRAULIC    MORTARS.          75 

the  same  percentages  rendered  24  per  cent  of  voids ;  it  may  be  added 
that  the  density  of  lime  mortars  is  not  influenced  much  by  the  pro- 
portions of  the  mixture ;  indeed,  the  rich  mortars  generally  are  more 
porous  than  those  of  an  average  degree  of  strength.  In  cement 
mortars,  however,  density  increases  in  proportion  to  the  percent- 
age of  cement,  and,  in  addition  to  the  advantages  of  density,  those 
of  strength  are  attained. 

If  rammed  concrete  is  employed  the  voids  may  be  still  further 
reduced.  The  advantages  of  concrete  as  compared  with  masonry 
are  also  shown  by  the  experiments  made  at  La  Rochelle.  As  its 
price  has  not  increased  appreciably,  it  is  easy  to  understand  that 
its  use  has  become  more  and  more  universal,  especially  in  foreign 
countries,  where  all  great  maritime  structures  have  been  carried 
out  in  cement  concrete. 

It  seems  surprising  that  blocks  of  neat  cement  should  have  been 
destroyed,  while  those  of  mixtures  of  1:2  have  stood  well.  Mor- 
tar made  of  neat  cement,  it  is  true,  is  of  great  density  and  in  a 
short  time  becomes  quite  impervious.  But  all  those  who  have 
made  any  tests  of  strength  with  such  mortars,  after  they  had  been 
exposed  to  sea  water,  will  know  how  fragile  they  become  after  a 
few  months.  Although  the  briquettes  do  not  show  any  outward 
sign  of  destruction,  they  have  become  as  brittle  as  glass  and  crack 
under  the  slightest  pressure ;  to  this  phenomenon,  which  doubtless 
must  be  attributed  to  excessive  crystallization,  is  due  the  distrac- 
tion of  neat  cement.  When  cement  contains  an  excess  of  lime 
(which  is  especially  the  case  when  gauged  neat)  the  phenomena  of 
expansion  make  their  appearance  with  greater  intensity,  and  de- 
struction is  rapid  even  in  calm  water.  As  soon  as  cement  is  mixed 
with  sand  this  fragility  disappears ;  after  four  years'  treatment  in 
sea  water,  for  instance,  we  found  neat  cement  to  have  only  6.4 
kilograms  crushing  strength  per  square  centimeter,  while  the  same 
brand  of  cement,  mixed  with  sand  in  the  proportion  of  1:1,  was 
found  to  have  54.7  kilograms  crushing  strength. 

Dr.  Michaelis,  whose  paper  we  have  mentioned  above,  believes 
that  the  solution  of  the  sea- water  problem  consists  in  mixing  a 
certain  percentage  of  trass  or  pozzuolana  with  Portland  cement. 
The  pozzuolana  will  combine  with  the  free  lime,  will  contribute 
towards  hardening,  and  will  prevent  the  lime  from  forming 
dangerous  compounds  under  the  influence  of  the  sulphate  of  mag- 
nesia contained  in  sea  water. 

According  to  Michaelis,  no  other  mortar  excels  a  mixture  of 
Portland  cement  and  trass  in  regard  to  price,  power  of  resistance, 
binding  qualities,  and  good  behavior  in  sea  water.  In  proof  of 
this  opinion,  he  has  made  a  long  series  of  experiments,  on  the 
basis  of  which  he  concludes  that  an  admixture  of  trass  to  cement 


76          INFLUENCE    OF    SEA    WATER   ON   HYDRAULIC    MORTARS. 

mortar  increases  its  strength,  and  also  its  resistance  to  decompo- 
sition. It  is  highly  probable  that  pozzuolaiias  will  combine  with 
the  lime  contained  in  cement,  and  the  interest  attached  to  the  ex- 
periments of  Dr.  Michaelis  can  not  be  denied.  But,  without  enter- 
ing into  a  detailed  discussion  of  his  conclusions,  we  will  demon- 
strate how  difficult  it  is  to  interpret  such  laboratory  tests. 

In  the  above-mentioned  paper  of  Alexandre  there  are  contained 
a  number  of  comparative  tests  of  mortars  gauged  with  different 
kinds  of  sand  and  immersed  in  sea  water.  Now,  the  sands  which 
rendered  a  very  considerable  increase  of  strength  and  which  pre- 
vented or  delayed  decomposition  of  mortars,  were  lime  sands. 
Here  no  chemical  influence  of  sand  can  be  considered,  as  carbonate 
of  lime  could  not  act  on  the  lime  becoming  free  during  gauging  and 
hardening.  These  results  have  been  confirmed  by  Feret's  tests ; 
the  tensile  strength  of  mortars  gauged  with  the  same  brand  of 
cement,  in  the  proportion  of  1:3,  after  one  year's  immersion  in  sea 
water,  was  found  to  be  25.7  kilograms  per  square  centimeter  where 
standard  sand  had  been  used,  39.5  kilograms  per  square  centimeter 
where  crushed  marble  had  been  used,  and  34.5  where  trass  had 
been  used.  Marble  has  therefore  rendered  more  strength  than 
trass ;  yet  there  is  in  this  case  no  chemical  action. 

Finally,  we  have  obtained  the  following  results  with  quartz 
sand,  about  whose  chemical  nonactivity  there  can  certainly  be  no 
doubt :  Standard  sand  mortar  1 : 3,  after  three  months'  hardening 
in  sea  water,  26.5  kilograms  per  square  centimeter;  standard  sand 
with  10  per  cent  fine  sand,  32.8  kilograms  per  square  centimeter; 
standard  sand  with  20  per  cent  fine  sand,  40.4  kilograms  per  square 
centimeter. 

If  exceedingly  fine  powder  of  any  kind  whatever  was  added  to 
the  sand,  we  have  invariably  noticed  an  increase  of  strength,  due 
solely  to  greater  density. 

All  these  tests  show,  therefore,  conclusively  that  in  all  admix- 
tures to  cement,  improvement  may  be  due  to  purely  physical  causes, 
and  there  is  nothing  to  show  that  admixtures  which  can  combine 
chemically  are  advantageous.  Conclusions  based  on  these  labora- 
tory tests  are  therefore  of  a  very  dubious  nature ;  there  are  too 
many  contradictory  points  not  yet  cleared  up,  and  time  frequently 
changes  even  those  opinions  which  were  considered  to  be  the  best 
founded. 

Is  the  lime  becoming  free  during  gauging  and  hardening  inju- 
rious? Is  it  advisable  to  mix  a  substance  with  the  cement  which 
will  combine  with  this  lime  ?  Do  the  pozzuolanas  exercise  a  bene- 
ficial influence?  It  can  not  be  said  that  any  actual  proof  has  been 
rendered. 


INFLUENCE   OF   SEA   WATER   ON   HYDRAULIC   MORTARS.          77 

The  faultless  behavior  of  Portland  cement  mortars  which  have 
been  exposed  to  sea  water  for  more  than  forty  years  shows  that 
they  will  resist  decomposition  without  any  admixture  of  pozzuo- 
lanas.  One  fact  has  certainly  been  demonstrated  beyond  a  doubt, 
viz,  that  mortars  should  be  as  impervious  as  possible.  This  leads 
to  very  simple  conclusions,  the  most  important  question  now  be- 
coming that  of  the  selection  of  sand. 

The  price  of  Portland  cement  has  depreciated  very  much,  and  no 
excessive  expenditure  is  required  even  for  mixtures  of  600  and  650 
kilograms  of  cement  to  1  cubic  meter  of  sand,  mixtures  which  appear 
to  be  necessary.  In  consideration  of  the  great  strength  of  these 
mortars,  great  savings  are  practicable  by  reducing  the  thickness  of 

walls. 

*  *  *  *  *  *  * 

Unfortunately,  good  sand  is  not  found  everywhere,  and  to  avoid 
the  cost  of  transportation,  it  is  frequently  necessary  to  employ  the 
sand  found  on  the  ground. 

In  his  paper  on  the  density  of  mortars,  Feret  says : 

We  arrive  at  the  conclusion  that  in  order  to  create  the  most  favorable  condi- 
tions for  the  resistance  of  mortars  to  the  destructive  action  of  sea  water,  the  use 
of  sand  containing  many  fine  grains  has  to  be  avoided  as  much  as  practicable, 
and  in  case  no  other  sand  is  available,  the  quantity  of  cement  used  for  gauging 
should  be  increased. 

We  believe  that  the  sand  question  should  be  still  further  explored. 
Fine  sand  must  decidedly  be  discarded,  and  only  very  good  sands  of 
known  origin  should  be  used. 

******* 

We  are  convinced  that  rich  mortars  gauged  -with  coarse  sand, 
and  the  exclusive  use  of  concrete,  will  produce  masonry  of  great 
power  of  resistance,  the  durability  of  which  may  be  taken  as  war- 
ranted. 


6"  ',•    :::V*..".-.VJ  A 


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